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OpenGL & Go Tutorial Part 1: Hello, OpenGL
============================================================
_[Part 1: Hello, OpenGL][6]_  |  _[Part 2: Drawing the Game Board][7]_  |  _[Part 3: Implementing the Game][8]_
_The full source code of the tutorial is available on [GitHub][9]._
### Introduction
[OpenGL][19] is pretty much the gold standard for any kind of graphics work, from desktop GUIs to games to mobile applications and even the web, I can almost guarantee you’ve viewed something rendered by OpenGL today. However, regardless of how popular and useful OpenGL is, it can be quite intimidating to get started compared to more high-level graphics libraries.
The purpose of this tutorial is to give you a starting point and basic understanding of OpenGL, and how to utilize it with [Go][20]. There are bindings for OpenGL in just about every language and Go is no exception with the [go-gl][21] packages, a full suite of generated OpenGL bindings for various OpenGL versions.
The tutorial will walk through a few phases outlined below, with our end goal being to implement [Conway’s Game of Life][22] using OpenGL to draw the game board in a desktop window. The full source code is available on GitHub at [github.com/KyleBanks/conways-gol][23] so feel free to check it out if you get stuck or use it as a reference if you decide to go your own way.
Before we get started, we need to get an understanding of what  _Conway’s Game of Life_  actually is. Here’s the summary from [Wikipedia][24]:
> The Game of Life, also known simply as Life, is a cellular automaton devised by the British mathematician John Horton Conway in 1970.
>
> The “game” is a zero-player game, meaning that its evolution is determined by its initial state, requiring no further input. One interacts with the Game of Life by creating an initial configuration and observing how it evolves, or, for advanced “players”, by creating patterns with particular properties.
>
> Rules
>
> The universe of the Game of Life is an infinite two-dimensional orthogonal grid of square cells, each of which is in one of two possible states, alive or dead, or “populated” or “unpopulated” (the difference may seem minor, except when viewing it as an early model of human/urban behaviour simulation or how one views a blank space on a grid). Every cell interacts with its eight neighbours, which are the cells that are horizontally, vertically, or diagonally adjacent. At each step in time, the following transitions occur:
>
> 1. Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
> 2. Any live cell with two or three live neighbours lives on to the next generation.
> 3. Any live cell with more than three live neighbours dies, as if by overpopulation.
> 4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
And without further ado, here’s a demo of what we’ll be building:
![Conway's Game of Life in OpenGL and Golang Tutorial - Demo Game](https://kylewbanks.com/images/post/golang-opengl-conway-1.gif)
In our simulation, a white cell indicates that it is alive, and black cell indicates that it is not.
### Outline
The tutorial is going to cover a lot of ground starting with the basics, however it will assume you have a minimal working knowledge of Go - at the very least you should know the basics of variables, slices, functions and structs, and have a working Go environment setup. I’ve developed the tutorial using Go version 1.8, but it should be compatible with previous versions as well. There is nothing particularly novel here in the Go implementation, so if you have experience in any similar programming language you should be just fine.
As for the tutorial, here’s what we’ll be covering:
* [Part 1: Hello, OpenGL][10]: Install and Setup OpenGL and [GLFW][11], Draw a Triangle to the Window
* [Part 2: Drawing the Game Board][12]: Make a Square out of Triangles, Draw a Grid of Squares covering the Window
* [Part 3: Implementing the Game][13]: Implement Conway’s Game
The final source code is available on [GitHub][25] but each  _Part_  includes a  _Checkpoint_  at the bottom containing the code up until that point. If anything is ever unclear or if you feel lost, check the bottom of the post for the full source!
Let’s get started!
### Install and Setup OpenGL and GLFW
We’ve introduced OpenGL but in order to use it we’re going to need a window to draw on to. [GLFW][26] is a cross-platform API for OpenGL that allows us to create and reference a window, and is also provided by the [go-gl][27] suite.
The first thing we need to do is decide on an OpenGL version. For the purposes of this tutorial we’ll use **OpenGL v4.1** but you can use **v2.1** just fine if your system doesn’t have the latest OpenGL versions. In order to install OpenGL we’ll do the following:
```
# For OpenGL 4.1
$ go get github.com/go-gl/gl/v4.1-core/gl
# Or 2.1
$ go get github.com/go-gl/gl/v2.1/gl
```
Next up, let’s install GLFW:
```
$ go get github.com/go-gl/glfw/v3.2/glfw
```
With these two packages installed, we’re ready to get started! We’re going to start by creating **main.go** and importing the packages (and a couple others we’ll need in a moment).
```
package main
import (
"log"
"runtime"
"github.com/go-gl/gl/v4.1-core/gl" // OR: github.com/go-gl/gl/v2.1/gl
"github.com/go-gl/glfw/v3.2/glfw"
)
```
Next lets define the **main** function, the purpose of which is to initialize OpenGL and GLFW and display the window:
```
const (
width = 500
height = 500
)
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
for !window.ShouldClose() {
// TODO
}
}
// initGlfw initializes glfw and returns a Window to use.
func initGlfw() *glfw.Window {
if err := glfw.Init(); err != nil {
panic(err)
}
glfw.WindowHint(glfw.Resizable, glfw.False)
glfw.WindowHint(glfw.ContextVersionMajor, 4) // OR 2
glfw.WindowHint(glfw.ContextVersionMinor, 1)
glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)
window, err := glfw.CreateWindow(width, height, "Conway's Game of Life", nil, nil)
if err != nil {
panic(err)
}
window.MakeContextCurrent()
return window
}
```
Alright let’s take a minute to walk through this and see what’s going on. First we define a couple constants, **width** and **height** - these will determine the size of the window, in pixels.
Next we have the **main** function. Here we instruct the **runtime** package to **LockOSThread()**, which ensures we will always execute in the same operating system thread, which is important for GLFW which must always be called from the same thread it was initialized on. Speaking of which, next we call **initGlfw** to get a window reference, and defer terminating. The window reference is then used in a for-loop where we say as long as the window should remain open, do  _something_ . We’ll come back to this in a bit.
**initGlfw** is our next function, wherein we call **glfw.Init()** to initialize the GLFW package. After that, we define some global GLFW properties, including disabling window resizing and the properties of our OpenGL version. Next it’s time to create a **glfw.Window** which is where we’re going to do our future drawing. We simply tell it the width and height we want, as well as a title, and then call **window.MakeContextCurrent**, binding the window to our current thread. Finally, we return the window.
If you build and run the program now, you should see… nothing. This makes sense, because we’re not actually doing anything with the window yet.
Let’s fix that by defining a new function that initializes OpenGL:
```
// initOpenGL initializes OpenGL and returns an intiialized program.
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
prog := gl.CreateProgram()
gl.LinkProgram(prog)
return prog
}
```
**initOpenGL**, like our **initGlfw** function above, initializes the OpenGL library and creates a  _program_ . A program gives us a reference to store shaders, which can then be used for drawing. We’ll come back to this in a bit, but for now just know that OpenGL is initialized and we have a **program** reference. We also print out the OpenGL version which can be helpful for debugging.
Back in **main**, let’s call this new function:
```
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
program := initOpenGL()
for !window.ShouldClose() {
draw(window, program)
}
}
```
You’ll notice now that we have our **program** reference, we’re calling a new **draw** function within our core window loop. Eventually this function will draw all of our cells to visualize the game state, but for now its just going to clear the window so we get a black screen:
```
func draw(window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(prog)
glfw.PollEvents()
window.SwapBuffers()
}
```
The first thing we do is call **gl.Clear** to remove anything from the window that was drawn last frame, giving us a clean slate. Next we tell OpenGL to use our program reference, which currently does nothing. Finally, we tell GLFW to check if there were any mouse or keyboard events (which we won’t be handling in this tutorial) with the **PollEvents** function, and tell the window to **SwapBuffers**. [Buffer swapping][28] is important because GLFW (like many graphics libraries) uses double buffering, meaning everything you draw is actually drawn to an invisible canvas, and only put onto the visible canvas when you’re ready - which in this case, is indicated by calling **SwapBuffers**.
Alright, we’ve covered a lot here, so let’s take a moment to see the fruits of our labors. Go ahead and run the program now, and you should get to see your first visual:
![Conway's Game of Life in OpenGL and Golang Tutorial - First Window](https://kylewbanks.com/images/post/golang-opengl-conway-2.png)
Beautiful.
### Draw a Triangle to the Window
We’ve made some serious progress, even if it doesn’t look like much, but we still need to actually draw something. We’ll start by drawing a triangle, which may at first seem like it would be more difficult to draw than the squares we’re eventually going to, but you’d be mistaken for thinking so. What you may not know is that triangles are probably the easiest shapes to draw, and in fact we’ll eventually be making our squares out of triangles anyways.
Alright so we want to draw a triangle, but how? Well, we draw shapes by defining the vertices of the shapes and providing them to OpenGL to be drawn. Let’s first define our triangle at the top of **main.go**:
```
var (
triangle = []float32{
0, 0.5, 0, // top
-0.5, -0.5, 0, // left
0.5, -0.5, 0, // right
}
)
```
This looks weird, but let’s break it down. First we have a slice of **float32**, which is the datatype we always use when providing vertices to OpenGL. The slice contains 9 values, three for each vertex of a triangle. The top line, **0, 0.5, 0**, is the top vertex represented as X, Y, and Z coordinates, the second line is the left vertex, and the third line is the right vertex. Each of these pairs of three represents the X, Y, and Z coordinates of the vertex relative to the center of the window, between **-1 and 1**. So the top point has an X of zero because its X is in the center of the window, a Y of  _0.5_  meaning it will be up one quarter (because the range is -1 to 1) of the window relative to the center of the window, and a Z of zero. For our purposes because we are drawing only in two dimensions, our Z values will always be zero. Now have a look at the left and right vertices and see if you can understand why they are defined as they are - it’s okay if it isn’t immediately clear, we’re going to see it on the screen soon enough so we’ll have a perfect visualization to play with.
Okay, we have a triangle defined, but now we need to draw it. In order to draw it, we need what’s called a **Vertex Array Object** or **vao** which is created from a set of points (what we defined as our triangle), and can be provided to OpenGL to draw. Let’s create a function called **makeVao** that we can provide with a slice of points and have it return a pointer to an OpenGL vertex array object:
```
// makeVao initializes and returns a vertex array from the points provided.
func makeVao(points []float32) uint32 {
var vbo uint32
gl.GenBuffers(1, &vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(points), gl.Ptr(points), gl.STATIC_DRAW)
var vao uint32
gl.GenVertexArrays(1, &vao)
gl.BindVertexArray(vao)
gl.EnableVertexAttribArray(0)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 0, nil)
return vao
}
```
First we create a **Vertex Buffer Object** or **vbo** to bind our **vao** to, which is created by providing the size (**4 x len(points)**) and a pointer to the points (**gl.Ptr(points)**). You may be wondering why it’s **4 x len(points)** - why not 6 or 3 or 1078? The reason is we are using **float32** slices, and a 32-bit float has 4 bytes, so we are saying the size of the buffer, in bytes, is 4 times the number of points.
Now that we have a buffer, we can create the **vao** and bind it to the buffer with **gl.BindBuffer**, and finally return the **vao**. This **vao** will then be used to draw the triangle!
Back in **main**:
```
func main() {
...
vao := makeVao(triangle)
for !window.ShouldClose() {
draw(vao, window, program)
}
}
Here we call **makeVao** to get our **vao** reference from the **triangle** points we defined before, and pass it as a new argument to the **draw** function:
func draw(vao uint32, window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(program)
gl.BindVertexArray(vao)
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(triangle) / 3))
glfw.PollEvents()
window.SwapBuffers()
}
```
Then we bind OpenGL to our **vao** so it knows what we’re talking above when we tell it to **DrawArrays**, and tell it the length of the triangle (divided by three, one for each X, Y, Z coordinate) slice so it knows how many vertices to draw.
If you run the application at this point you might be expecting to see a beautiful triangle in the center of the window, but unfortunately you would be mistaken. There’s still one thing left to do, you see we’ve told OpenGL that we want to draw a triangle, but we need to tell it  _how_  to draw the triangle.
In order to do that, we need what are called fragment and vertex shaders, which are quite advanced and beyond the scope of this tutorial (and honestly, beyond the scope of my OpenGL knowledge), however [Harold Serrano on Quora][29] gives a wonderful explanation of what they are. All we absolutely need to understand for this application is that shaders are their own mini-programs (written in [OpenGL Shader Language or GLSL][30]) that manipulate vertices to be drawn by OpenGL, and are used to (for example) determine the color of a shape.
We start by adding two more imports and a function called **compileShader**:
```
import (
"strings"
"fmt"
)
func compileShader(source string, shaderType uint32) (uint32, error) {
shader := gl.CreateShader(shaderType)
csources, free := gl.Strs(source)
gl.ShaderSource(shader, 1, csources, nil)
free()
gl.CompileShader(shader)
var status int32
gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
if status == gl.FALSE {
var logLength int32
gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLength)
log := strings.Repeat("\x00", int(logLength+1))
gl.GetShaderInfoLog(shader, logLength, nil, gl.Str(log))
return 0, fmt.Errorf("failed to compile %v: %v", source, log)
}
return shader, nil
}
```
The purpose of this function is to receive the shader source code as a string as well as its type, and return a pointer to the resulting compiled shader. If it fails to compile we’ll get an error returned containing the details.
Now let’s define the shaders and compile them from **makeProgram**. Back up in our **const** block where we define **width** and **height**:
```
vertexShaderSource = `
#version 410
in vec3 vp;
void main() {
gl_Position = vec4(vp, 1.0);
}
` + "\x00"
fragmentShaderSource = `
#version 410
out vec4 frag_colour;
void main() {
frag_colour = vec4(1, 1, 1, 1);
}
` + "\x00"
```
As you can see these are strings containing GLSL source code for two shaders, one for a  _vertex shader_  and another for a  _fragment shader_ . The only thing special about these strings is that they both end in a null-termination character, **\x00** - a requirement for OpenGL to be able to compile them. Make note of the **fragmentShaderSource**, this is where we define the color of our shape in RGBA format using a **vec4**. You can change the value here, which is currently **RGBA(1, 1, 1, 1)** or  _white_ , to change the color of the triangle.
Also of note is that both programs start with **#version 410**, which you should change to **#version 120** if using OpenGL 2.1. **120** is not a typo - use **120** not **210** if you’re on OpenGL 2.1!
Next in **initOpenGL** we’ll compile the shaders and attach them to our **program**:
```
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
if err != nil {
panic(err)
}
fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
if err != nil {
panic(err)
}
prog := gl.CreateProgram()
gl.AttachShader(prog, vertexShader)
gl.AttachShader(prog, fragmentShader)
gl.LinkProgram(prog)
return prog
}
```
Here we call our **compileShader** function with the  _vertex shader_ , specifying its type as a **gl.VERTEX_SHADER**, and do the same with the  _fragment shader_  but specifying its type as a **gl.FRAGMENT_SHADER**. After compiling them, we attach them to our program by calling **gl.AttachShader** with our program and each compiled shader.
And now we’re finally ready to see our glorious triangle! Go ahead and run, and if all is well you’ll see:
![Conway's Game of Life in OpenGL and Golang Tutorial - Hello, Triangle!](https://kylewbanks.com/images/post/golang-opengl-conway-3.png)
### Summary
Amazing, right! All that for a single triangle, but I promise you we’ve setup the majority of the OpenGL code that will serve us for the rest of the tutorial. I highly encourage you to take a few minutes to play with the code and see if you can move, resize, and change the color of the triangle. OpenGL can be  _very_  intimidating, and it can feel at times like its difficult to understand what’s going on, but understand that this isn’t magic - it only looks like it is.
In the next part of the tutorial we’ll make a square out of two right-angled triangles - see if you can try and figure this part out before moving on. If not, don’t worry because we’ll be walking through the code in [Part 2][31], followed by creating a full grid of squares that will act as our game board.
Finally, in [Part 3][32] we continue by using the grid to implement  _Conway’s Game of Life!_
_[Part 1: Hello, OpenGL][14]_  |  _[Part 2: Drawing the Game Board][15]_  |  _[Part 3: Implementing the Game][16]_
_The full source code of the tutorial is available on [GitHub][17]._
### Checkpoint
Here’s the contents of **main.go** at this point of the tutorial:
```
package main
import (
"fmt"
"log"
"runtime"
"strings"
"github.com/go-gl/gl/v4.1-core/gl" // OR: github.com/go-gl/gl/v2.1/gl
"github.com/go-gl/glfw/v3.2/glfw"
)
const (
width = 500
height = 500
vertexShaderSource = `
#version 410
in vec3 vp;
void main() {
gl_Position = vec4(vp, 1.0);
}
` + "\x00"
fragmentShaderSource = `
#version 410
out vec4 frag_colour;
void main() {
frag_colour = vec4(1, 1, 1, 1.0);
}
` + "\x00"
)
var (
triangle = []float32{
0, 0.5, 0,
-0.5, -0.5, 0,
0.5, -0.5, 0,
}
)
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
program := initOpenGL()
vao := makeVao(triangle)
for !window.ShouldClose() {
draw(vao, window, program)
}
}
func draw(vao uint32, window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(program)
gl.BindVertexArray(vao)
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(triangle)/3))
glfw.PollEvents()
window.SwapBuffers()
}
// initGlfw initializes glfw and returns a Window to use.
func initGlfw() *glfw.Window {
if err := glfw.Init(); err != nil {
panic(err)
}
glfw.WindowHint(glfw.Resizable, glfw.False)
glfw.WindowHint(glfw.ContextVersionMajor, 4)
glfw.WindowHint(glfw.ContextVersionMinor, 1)
glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)
window, err := glfw.CreateWindow(width, height, "Conway's Game of Life", nil, nil)
if err != nil {
panic(err)
}
window.MakeContextCurrent()
return window
}
// initOpenGL initializes OpenGL and returns an intiialized program.
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
if err != nil {
panic(err)
}
fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
if err != nil {
panic(err)
}
prog := gl.CreateProgram()
gl.AttachShader(prog, vertexShader)
gl.AttachShader(prog, fragmentShader)
gl.LinkProgram(prog)
return prog
}
// makeVao initializes and returns a vertex array from the points provided.
func makeVao(points []float32) uint32 {
var vbo uint32
gl.GenBuffers(1, &vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(points), gl.Ptr(points), gl.STATIC_DRAW)
var vao uint32
gl.GenVertexArrays(1, &vao)
gl.BindVertexArray(vao)
gl.EnableVertexAttribArray(0)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 0, nil)
return vao
}
func compileShader(source string, shaderType uint32) (uint32, error) {
shader := gl.CreateShader(shaderType)
csources, free := gl.Strs(source)
gl.ShaderSource(shader, 1, csources, nil)
free()
gl.CompileShader(shader)
var status int32
gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
if status == gl.FALSE {
var logLength int32
gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLength)
log := strings.Repeat("\x00", int(logLength+1))
gl.GetShaderInfoLog(shader, logLength, nil, gl.Str(log))
return 0, fmt.Errorf("failed to compile %v: %v", source, log)
}
return shader, nil
}
```
Let me know if this post was helpful on Twitter [@kylewbanks][33] or down below, and follow me to keep up with future posts!
--------------------------------------------------------------------------------
via: https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
作者：[kylewbanks ][a]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]:https://twitter.com/kylewbanks
[1]:https://kylewbanks.com/category/golang
[2]:https://kylewbanks.com/category/opengl
[3]:https://twitter.com/intent/tweet?text=OpenGL%20%26%20Go%20Tutorial%20Part%201%3A%20Hello%2C%20OpenGL%20https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl%20by%20%40kylewbanks
[4]:mailto:?subject=Check%20Out%20%22OpenGL%20%26%20Go%20Tutorial%20Part%201%3A%20Hello%2C%20OpenGL%22&body=https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl
[5]:https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl
[6]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[7]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[8]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[9]:https://github.com/KyleBanks/conways-gol
[10]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[11]:http://www.glfw.org/
[12]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[13]:https://kylewbanks.com/blog/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[14]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[15]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[16]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[17]:https://github.com/KyleBanks/conways-gol
[18]:https://twitter.com/kylewbanks
[19]:https://www.opengl.org/
[20]:https://golang.org/
[21]:https://github.com/go-gl/gl
[22]:https://en.wikipedia.org/wiki/Conway's_Game_of_Life
[23]:https://github.com/KyleBanks/conways-gol
[24]:https://en.wikipedia.org/wiki/Conway's_Game_of_Life
[25]:https://github.com/KyleBanks/conways-gol
[26]:http://www.glfw.org/
[27]:https://github.com/go-gl/glfw
[28]:http://www.glfw.org/docs/latest/window_guide.html#buffer_swap
[29]:https://www.quora.com/What-is-a-vertex-shader-and-what-is-a-fragment-shader/answer/Harold-Serrano?srid=aVb
[30]:https://www.opengl.org/sdk/docs/tutorials/ClockworkCoders/glsl_overview.php
[31]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[32]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[33]:https://twitter.com/kylewbanks

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OpenGL 与 Go 教程 第一节: Hello, OpenGL
============================================================
_[第一节: Hello, OpenGL][6]_  |  _[第二节: 绘制游戏面板][7]_  |  _[第三节: 实现游戏功能][8]_
_这篇教程的所有源代码都可以在 [GitHub][9] 上找到。_
### 介绍
[OpenGL][19] 是一门相当好的技术，适用于多种类型的绘图工作，从桌面的 GUI 到游戏，到移动应用甚至 web 应用。我敢保证，你今天看到的图形有些就是用 OpenGL 渲染的。可是，不管 OpenGL 多受欢迎、有多好用，与学习其它高层次的绘图库相比，学习 OpenGL 是要相当足够的决心的。
这个教程的目的是给你一个切入点，让你对 OpenGL 有个基本的了解，然后教你怎么用 [Go][20] 操作它。几乎每种编程语言都有绑定 OpenGL 的库，Go 也不例外，它有 [go-gl][21] 这个包。这是一个完整的套件，可以绑定 OpenGL ，适用于多种版本的 OpenGL。
这篇教程会按照下面列出的几个阶段进行介绍，我们最终的目标是用 OpenGL 在桌面窗口绘制游戏面板，进而实现 [Conway's Game of Life][22]。完整的源代码可以在 GitHub [github.com/KyleBanks/conways-gol][23] 上获得，当你有疑惑的时候可以随时查看源代码，或者你要按照自己的方式学习也可以参考这个代码。
在我们开始之前，我们要先弄明白 _Conway's Game of Life_ 到底是什么。这里是 [Wikipedia][24] 上面的总结：
> 《Game of Life》，也可以简称为 Life，是一个细胞自动变化的过程，由英国数学家 John Horton Conway 于 1970 年提出。
>
> 这个“游戏”没有玩家，也就是说它的发展依靠的是它的初始状态，不需要输入。用户通过创建初始配置文件、观察它如何演变，或者对于高级“玩家”可以创建特殊属性的模式，进而与《Game of Life》进行交互。
>
> 规则
>
> 《Game of Life》的世界是一个无穷多的二维正交的正方形细胞的格子，每一个格子都有两种可能的状态，“存活”或者“死亡”，也可以说是“填充态”或“未填充态”（区别可能很小，除非把它看作一个模拟人类/哺乳动物行为的早期模型，或者在一个人如何看待方格里的空白时）。每一个细胞与它周围的八个细胞相关联，这八个细胞分别是水平、垂直、斜对角相接的。在游戏中的每一步，下列事情中的一件将会发生：
>
> 1. 任何存活着的细胞当任何一个存活的 cell 的附近少于 2 个存活的 cell 时，该 cell 将会消亡，就像人口过少所导致的结果一样
> 2. 当任何一个存活的 cell 的附近有 2 至 3 个存活的 cell 时，该 cell 在下一代中仍然存活。
> 3. 当任何一个存活的 cell 的附近多于 3 个存活的 cell 时，该 cell 将会消亡，就像人口过多所导致的结果一样
> 4. 任何一个消亡的 cell 附近刚好有 3 个存活的 cell，该 cell 会变为存活的状态，就像重生一样。
不需要其他工具，这里由一个我们将会制作的演示程序：
![OpenGL 与 Go 语言教程中的 Conway's Game of Life - 示例游戏](https://kylewbanks.com/images/post/golang-opengl-conway-1.gif)
在我们的运行过程中，白色的细胞表示它是存活着的，黑色的细胞表示它已经死亡。
### 概述
本教程将会涉及到很多基础内容，从最基本的开始，但是你还是要对 Go 由一些最基本的了解 - 至少你应该知道变量，切片，函数和结构体，并且装了一个 Go 的运行环境。我写这篇教程用的 Go 版本是 1.8，但它应该与之前的版本兼容。这里用 Go 语言实现没有什么特别新奇的东西，因此只要你有过类似的编程经历就行。
这里是我们在这个教程里将会讲到的东西：
* [第一节: Hello, OpenGL][10]: 安装 OpenGL 和 [GLFW][11]，在窗口上绘制一个三角形。
* [第二节: 绘制游戏面板][12]: 用三角形拼成方形，在窗口上用方形绘成格子。
* [第三节: 实现游戏功能][13]: 实现 Conway 游戏
最后的源代码可以在 [GitHub][25] 上获得，每一节的末尾有个_回顾_，包含该节相关的代码。如果有什么不清楚的地方或者是你感到疑惑的，看看每一节末尾的完整代码。
现在就开始吧！
### 安装 OpenGL 和 GLFW
我们介绍过 OpenGL，但是为了使用它，我们要有个窗口可以绘制东西。 [GLFW][26] 是一款对于 OpenGL 跨平台的 API，允许我们创建窗口并使用，而且它是 [go-gl][27] 套件中提供的。
我们要做的第一件事就是确定 OpenGL 的版本。为了方便本教程，我们将会使用 **OpenGL v4.1**，但你也可以用 **v2.1** 要是你的操作系统不支持最新的 OpenGL。要安装 OpenGL，我们需要做这些事：
```
# 对于 OpenGL 4.1
$ go get github.com/go-gl/gl/v4.1-core/gl
# 或者 2.1
$ go get github.com/go-gl/gl/v2.1/gl
```
然后是安装 GLFW：
```
$ go get github.com/go-gl/glfw/v3.2/glfw
```
安装好这两个包之后，我们就可以开始了！先创建 **main.go** 文件，导入相应的包（我们待会儿会用到的其他东西）。
```
package main
import (
"log"
"runtime"
"github.com/go-gl/gl/v4.1-core/gl" // OR: github.com/go-gl/gl/v2.1/gl
"github.com/go-gl/glfw/v3.2/glfw"
)
```
Next lets define the **main** function, the purpose of which is to initialize OpenGL and GLFW and display the window:
接下来定义一个叫做 **main** 的函数，这是用来初始化 OpenGL 以及 GLFW，显示窗口的：
```
const (
width = 500
height = 500
)
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
for !window.ShouldClose() {
// TODO
}
}
// initGlfw 初始化 glfw 并且返回一个可用的窗口。
func initGlfw() *glfw.Window {
if err := glfw.Init(); err != nil {
panic(err)
}
glfw.WindowHint(glfw.Resizable, glfw.False)
glfw.WindowHint(glfw.ContextVersionMajor, 4) // OR 2
glfw.WindowHint(glfw.ContextVersionMinor, 1)
glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)
window, err := glfw.CreateWindow(width, height, "Conway's Game of Life", nil, nil)
if err != nil {
panic(err)
}
window.MakeContextCurrent()
return window
}
```
好了，让我们花一分钟来运行一下这个程序，看看会发生什么。首先定义了一些常量， **width** 和 **height** - 它们决定窗口的像素大小。
然后就是 **main** 函数。这里我们使用了 **runtime** 包的 **LockOSThread()**，这能确保我们总是在操作系统的一个线程中运行代码，这对 GLFW 来说很重要，GLFW 被初始化之后需要在同一个进程里被调用多次。讲完这个，接下来我们调用 **initGlfw** 来获得一个窗口的引用，并且 defer glfw 的 terminating 方法。窗口的引用会被用在一个 for 循环中，只要窗口是打开的状态，就执行某些事情。我们待会儿会讲要做的事情是什么。
**initGlfw** 是另一个函数，这里我们调用 **glfw.Init()** 来初始化 GLFW 包。然后我们定义了 GLFW 的一些全局属性，包括禁用调整窗口大小和改变 OpenGL 的属性。然后创建了 **glfw.Window**，这会在稍后的绘图中用到。我们仅仅告诉它我们想要的宽度和高度，以及标题，然后调用 **window.MakeContextCurrent**，将窗口绑定到当前的进程中。最后就是返回窗口的引用了。
如果你现在就构建、运行这个程序，你看不到任何东西。很合理，因为我们还没有用这个窗口做什么实质性的事。
定义一个新函数，初始化 OpenGL，就可以解决这个问题：
```
// initOpenGL 初始化 OpenGL 并且返回一个初始化了的程序。
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
prog := gl.CreateProgram()
gl.LinkProgram(prog)
return prog
}
```
**initOpenGL** 就像之前的 **initGlfw** 函数一样，初始化 OpenGL 库，创建一个_程序_。这个程序是一个包含了着色器的引用，稍后会用于绘图。待会儿会讲这一点，现在只用知道 OpenGL 已经初始化完成了，我们有一个 **program** 的引用。我们还打印了 OpenGL 的版本，这对于 debug 很有帮助。
回到 **main** 函数里，调用这个新函数：
```
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
program := initOpenGL()
for !window.ShouldClose() {
draw(window, program)
}
}
```
你应该注意到了现在我们有 **program** 的引用，在我们的窗口循环中，调用新的 **draw** 函数。最终这个函数会绘制出所有细胞，让游戏状态变得可视化，但是现在它做的仅仅是情况窗口，所以我们只能看到一个全黑的屏幕：
```
func draw(window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(prog)
glfw.PollEvents()
window.SwapBuffers()
}
```
我们首先做的是调用 **gl.clear** 函数来清除上一帧在窗口中绘制的东西，给我们一个干净的面板。然后我们告诉 OpenGL 去使用程序引用，这个引用还没有做什么事。最终我们告诉 GLFW 用 **PollEvents** 去检查是否有鼠标或者键盘事件（这一节里还不会对这些事件进行处理），告诉窗口 **SwapBuffers**。 [Buffer swapping][28](交换缓冲区) 很重要，因为 GLFW（像其他图形库一样）使用双缓冲，也就是说你绘制的所有东西实际上是绘制到一个不可见的画布上，当你准备好进行展示的时候就把绘制的这些东西放到可见的画布中 - 这种情况下，就需要调用 **SwapBuffers** 函数。
好了，到这里我们已经讲了很多东西，花一点时间看看我们的实验成果。运行这个程序，你应该可以看到你所绘制的第一个东西：
![OpenGL 与 Go 语言教程中的 Conway's Game of Life - 第一个窗口](https://kylewbanks.com/images/post/golang-opengl-conway-2.png)
完美！
### 在窗口里绘制三角形
我们已经完成了一些复杂的步骤，即使看上去和图片不像，但我们仍然需要绘制一些东西。我们会以三角形绘制开始，可能这第一眼看上去要比我们最终要绘制的方形更难，但你会知道这样的想法是错的。你可能不知道的是三角形或许是绘制的图形中最简单的，实际上我们最终会用某种方式把三角形拼成方形。
好吧，那么我们想要绘制一个三角形，怎么做呢？我们通过定义图形的顶点来绘制图形，把它们交给 OpenGL 来进行绘制。先在 **main.go** 的顶部里定义我们的三角形：
```
var (
triangle = []float32{
0, 0.5, 0, // top
-0.5, -0.5, 0, // left
0.5, -0.5, 0, // right
}
)
```
这看上去很奇怪，让我们分开来看。首先我们用了一个 **float32** 切片（slice），这是一种我们总会在向 OpenGL 传递顶点时用到的数据类型。这个切片包含 9 个值，每三个值构成三角形的一个点。第一行， **0， 0.5， 0** 表示的是 X、Y、Z 坐标，是最上方的顶点，第二行是左边的顶点，第三行是右边的顶点。每一组的三个点都表示相对于窗口中心点的 X、Y、Z 坐标，在 **-1 和 1** 之间。因此最上面的顶点 X 坐标是 0，因为它在 X 方向上位于窗口中央，Y 坐标是 _0.5_ 意味着它会相对窗口中央上移 1/4 个单位（因为窗口的范围是 -1 到 1），Z 坐标是 0.因为我们只需要在二维空间中绘图，所以 Z 值永远是 0。现在看一看左右两边的顶点，看看你能不能理解为什么它们是这样定义的 —— 如果不能立刻就弄清楚也没关系，我们将会在屏幕上去观察它，因此我们需要一个完美的图形来进行观察。
好了，我们定义了一个三角形，但是现在我们得把它画出来。要画出这个三角形，我们需要一个叫做 **Vertex Array Object** 或者叫 **vao** 的东西，这是由一系列的点（也就是我们定义的三角形）创造的，这个东西可以提供给 OpenGL 来进行绘制。创建一个叫做 **makeVao** 的函数，然后我们可以提供一组切片的点，让它返回一个指向 OpenGL vertex array object 的指针：
```
// makeVao 执行初始化并从提供的点里面返回一个顶点数组
func makeVao(points []float32) uint32 {
var vbo uint32
gl.GenBuffers(1, &vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(points), gl.Ptr(points), gl.STATIC_DRAW)
var vao uint32
gl.GenVertexArrays(1, &vao)
gl.BindVertexArray(vao)
gl.EnableVertexAttribArray(0)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 0, nil)
return vao
}
```
首先我们创造了 **Vertex Buffer Object** 或者说 **vbo** 绑定到我们的 **vao** 上，**vbo** 是通过所占空间（也就是**4 x len(points)**大小的空间）和一个指向顶点的指针（**gl.Ptr(points)**）来创建的。你也许会好奇为什么它是 **4 x len(points)** - 而不是 6 或者 3 或者 1078 呢？原因在于我们用的是 **float32** 切片，32 个 bit 的 float 浮点型变量是 4 个字节，因此我们说这个缓冲区以字节为单位的大小是点个数的 4 倍。
现在我们有缓冲区了，可以创建 **vao** 并用 **gl.BindBuffer** 把它绑定到缓冲区上，最后返回 **vao**。这个 **vao** 将会被用于绘制三角形！
回到 **main** 函数:
```
func main() {
...
vao := makeVao(triangle)
for !window.ShouldClose() {
draw(vao, window, program)
}
}
这里我们调用了 **makeVao** ，从我们之前定义的 **triangle** 顶点中获得 **vao** 引用，将它作为一个新的参数传递给 **draw** 函数：
func draw(vao uint32, window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(program)
gl.BindVertexArray(vao)
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(triangle) / 3))
glfw.PollEvents()
window.SwapBuffers()
}
```
然后我们把 OpenGL 绑定到 **vao** 上，这样当我们告诉 OpenGL 三角形切片的顶点数（除以 3，是因为每一个点有 X、Y、Z 坐标），让它去 **DrawArrays** ，它就知道要画多少个顶点了。
如果你这时候运行程序，你可能希望在窗口中央看到一个美丽的三角形，但是不幸的是你还看不到。还有一件事情没做，我们告诉 OpenGL 我们要画一个三角形，但是我们还要告诉它_怎么_画出来。
要让它画出来，我们需要叫做片元着色器和顶点着色器的东西，这些已经超出本教程的范围了（老实说，也超出了我对 OpenGL 的了解），但 [Harold Serrano On Quora][29] 关于它们是什么给出了完美的介绍。我们只需要理解，对于这个应用来说，着色器是它内部的小程序（用 [OpenGL Shader Language or GLSL][30] 编写的），操作顶点进行绘制，也可用于确定图形的颜色。
添加两个 imports 和一个叫做 **compileShader** 的函数：
```
import (
"strings"
"fmt"
)
func compileShader(source string, shaderType uint32) (uint32, error) {
shader := gl.CreateShader(shaderType)
csources, free := gl.Strs(source)
gl.ShaderSource(shader, 1, csources, nil)
free()
gl.CompileShader(shader)
var status int32
gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
if status == gl.FALSE {
var logLength int32
gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLength)
log := strings.Repeat("\x00", int(logLength+1))
gl.GetShaderInfoLog(shader, logLength, nil, gl.Str(log))
return 0, fmt.Errorf("failed to compile %v: %v", source, log)
}
return shader, nil
}
```
这个函数的目的是以字符串的形式接受着色器源代码和它的类型，然后返回一个指向这个编译好的着色器的指针。如果编译失败，我们就会获得出错的详细信息。
现在定义着色器，在 **makeProgram** 里编译。回到我们的 **const** 块中，我们在这里定义了 **width** 和 **hegiht**。
```
vertexShaderSource = `
#version 410
in vec3 vp;
void main() {
gl_Position = vec4(vp, 1.0);
}
` + "\x00"
fragmentShaderSource = `
#version 410
out vec4 frag_colour;
void main() {
frag_colour = vec4(1, 1, 1, 1);
}
` + "\x00"
```
你能看到这是两个着色器程序，包含了 GLSL 源代码的字符串，一个是_顶点着色器_，另一个是_片元着色器_。唯一比较特殊的地方是它们都要在末尾加上一个空终止字符，**\x00** —— OpenGL 需要它才能编译着色器。注意 **fragmentShaderSource**，这是我们用 RGBA 形式的值通过 **vec4** 来定义我们图形的颜色。你可以修改这里的值来改变这个三角形的颜色，现在的值是 **RGBA(1, 1, 1, 1)** 或者说是 _white_。
同样需要注意的是这两个程序都是运行在 **#version 410** 版本下，如果你用的是 OpenGL 2.1，那你也可以改成 **#version 120**。**120** 不是打错的，如果你用的是 OpenGL 2.1，要用 **120** 而不是 **210**！
接下来在 **initOpenGL** 中我们会编译着色器，把它们附加到我们的 **program** 中。
```
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
if err != nil {
panic(err)
}
fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
if err != nil {
panic(err)
}
prog := gl.CreateProgram()
gl.AttachShader(prog, vertexShader)
gl.AttachShader(prog, fragmentShader)
gl.LinkProgram(prog)
return prog
}
```
这里我们用 _顶点着色器_ 调用了 **compileShader** 函数，指定它的类型是 **gl.VERTEX_SHADER**，对 _片元着色器_ 做了同样的事情，但是指定的类型是 **gl.FRAGMENT_SHADER**。编译完成后，我们把它们附加到程序中，调用 **gl.AttachShader**，传递程序以及编译好的着色器。
现在我们终于可以看到我们漂亮的三角形了！运行程序，如果一切顺利的话你会看到这些：
![OpenGL 与 Go 语言教程中的 Conway's Game of Life - Hello, Triangle!](https://kylewbanks.com/images/post/golang-opengl-conway-3.png)
### 总结
是不是很惊喜！这些代码画出了一个三角形，但我保证我们已经完成了大部分的 OpenGL 代码，在接下来的章节中我们还会用到这些代码。我十分推荐你花几分钟修改一下代码，看看你能不能移动三角形，改变三角形的大小和颜色。OpenGL 可以令人心生畏惧，有时想要理解发生了什么很困难，但是要记住，这不是魔术 - 它就是它看上去的东西。
下一节里我们讲会用两个锐角三角形拼出一个方形 - 看看你能不能试着修改这一节的代码，再进入下一节。不能也没有关系，因为我们在 [第二节][31] 还会编写代码， 按照创建一个有许多方形的格子，我们把它当做游戏面板。
最后，在[第三节][32] 里我们会用格子来实现 _Conway’s Game of Life_！
_[第一节: Hello, OpenGL][14]_ | _[第二节: 绘制游戏面板][15]_ | _[第三节：实现游戏功能][16]_
_本教程的完整源代码可在 [GitHub][17] 上获得。_
### 回顾
本教程 **main.go** 文件的内容如下：
```
package main
import (
"fmt"
"log"
"runtime"
"strings"
"github.com/go-gl/gl/v4.1-core/gl" // OR: github.com/go-gl/gl/v2.1/gl
"github.com/go-gl/glfw/v3.2/glfw"
)
const (
width = 500
height = 500
vertexShaderSource = `
#version 410
in vec3 vp;
void main() {
gl_Position = vec4(vp, 1.0);
}
` + "\x00"
fragmentShaderSource = `
#version 410
out vec4 frag_colour;
void main() {
frag_colour = vec4(1, 1, 1, 1.0);
}
` + "\x00"
)
var (
triangle = []float32{
0, 0.5, 0,
-0.5, -0.5, 0,
0.5, -0.5, 0,
}
)
func main() {
runtime.LockOSThread()
window := initGlfw()
defer glfw.Terminate()
program := initOpenGL()
vao := makeVao(triangle)
for !window.ShouldClose() {
draw(vao, window, program)
}
}
func draw(vao uint32, window *glfw.Window, program uint32) {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(program)
gl.BindVertexArray(vao)
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(triangle)/3))
glfw.PollEvents()
window.SwapBuffers()
}
// initGlfw 初始化 glfw 并返回一个窗口供使用。
func initGlfw() *glfw.Window {
if err := glfw.Init(); err != nil {
panic(err)
}
glfw.WindowHint(glfw.Resizable, glfw.False)
glfw.WindowHint(glfw.ContextVersionMajor, 4)
glfw.WindowHint(glfw.ContextVersionMinor, 1)
glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)
window, err := glfw.CreateWindow(width, height, "Conway's Game of Life", nil, nil)
if err != nil {
panic(err)
}
window.MakeContextCurrent()
return window
}
// initOpenGL 初始化 OpenGL 并返回一个已经编译好的着色器程序
func initOpenGL() uint32 {
if err := gl.Init(); err != nil {
panic(err)
}
version := gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", version)
vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
if err != nil {
panic(err)
}
fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
if err != nil {
panic(err)
}
prog := gl.CreateProgram()
gl.AttachShader(prog, vertexShader)
gl.AttachShader(prog, fragmentShader)
gl.LinkProgram(prog)
return prog
}
// makeVao 执行初始化并从提供的点里面返回一个顶点数组
func makeVao(points []float32) uint32 {
var vbo uint32
gl.GenBuffers(1, &vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(points), gl.Ptr(points), gl.STATIC_DRAW)
var vao uint32
gl.GenVertexArrays(1, &vao)
gl.BindVertexArray(vao)
gl.EnableVertexAttribArray(0)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 0, nil)
return vao
}
func compileShader(source string, shaderType uint32) (uint32, error) {
shader := gl.CreateShader(shaderType)
csources, free := gl.Strs(source)
gl.ShaderSource(shader, 1, csources, nil)
free()
gl.CompileShader(shader)
var status int32
gl.GetShaderiv(shader, gl.COMPILE_STATUS, &status)
if status == gl.FALSE {
var logLength int32
gl.GetShaderiv(shader, gl.INFO_LOG_LENGTH, &logLength)
log := strings.Repeat("\x00", int(logLength+1))
gl.GetShaderInfoLog(shader, logLength, nil, gl.Str(log))
return 0, fmt.Errorf("failed to compile %v: %v", source, log)
}
return shader, nil
}
```
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[a]:https://twitter.com/kylewbanks
[1]:https://kylewbanks.com/category/golang
[2]:https://kylewbanks.com/category/opengl
[3]:https://twitter.com/intent/tweet?text=OpenGL%20%26%20Go%20Tutorial%20Part%201%3A%20Hello%2C%20OpenGL%20https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl%20by%20%40kylewbanks
[4]:mailto:?subject=Check%20Out%20%22OpenGL%20%26%20Go%20Tutorial%20Part%201%3A%20Hello%2C%20OpenGL%22&body=https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl
[5]:https://www.facebook.com/sharer/sharer.php?u=https%3A%2F%2Fkylewbanks.com%2Fblog%2Ftutorial-opengl-with-golang-part-1-hello-opengl
[6]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[7]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[8]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[9]:https://github.com/KyleBanks/conways-gol
[10]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[11]:http://www.glfw.org/
[12]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[13]:https://kylewbanks.com/blog/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[14]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-1-hello-opengl
[15]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[16]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[17]:https://github.com/KyleBanks/conways-gol
[18]:https://twitter.com/kylewbanks
[19]:https://www.opengl.org/
[20]:https://golang.org/
[21]:https://github.com/go-gl/gl
[22]:https://en.wikipedia.org/wiki/Conway's_Game_of_Life
[23]:https://github.com/KyleBanks/conways-gol
[24]:https://en.wikipedia.org/wiki/Conway's_Game_of_Life
[25]:https://github.com/KyleBanks/conways-gol
[26]:http://www.glfw.org/
[27]:https://github.com/go-gl/glfw
[28]:http://www.glfw.org/docs/latest/window_guide.html#buffer_swap
[29]:https://www.quora.com/What-is-a-vertex-shader-and-what-is-a-fragment-shader/answer/Harold-Serrano?srid=aVb
[30]:https://www.opengl.org/sdk/docs/tutorials/ClockworkCoders/glsl_overview.php
[31]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-2-drawing-the-game-board
[32]:https://kylewbanks.com/blog/tutorial-opengl-with-golang-part-3-implementing-the-game
[33]:https://twitter.com/kylewbanks