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test_opengles3.go
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test_opengles3.go
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/*
Compile: go build -tags=gles2 -x -v test_opengles3.1.go
*/
package main
import (
"fmt"
gl "github.com/leonkasovan/gl/v3.1/gles2"
"github.com/veandco/go-sdl2/sdl"
"runtime"
)
const (
vertexShaderSource = `
#version 300 es
precision mediump float;
in vec3 position;
void main() {
gl_Position = vec4(position, 1.0);
}
`
fragmentShaderSource = `
#version 300 es
precision mediump float;
out vec4 FragColor;
void main() {
FragColor = vec4(1.0, 0.5, 0.2, 1.0);
}
`
)
var (
vertices = []float32{
-0.5, -0.5, 0.0,
0.5, -0.5, 0.0,
0.0, 0.5, 0.0,
}
)
func main() {
runtime.LockOSThread()
var err error
// SDL2 initialization
if err = sdl.Init(sdl.INIT_EVERYTHING); err != nil {
panic(err)
}
defer sdl.Quit()
// Set OpenGL version
sdl.GLSetAttribute(sdl.GL_CONTEXT_MAJOR_VERSION, 3)
sdl.GLSetAttribute(sdl.GL_CONTEXT_MINOR_VERSION, 1)
sdl.GLSetAttribute(sdl.GL_CONTEXT_PROFILE_MASK, sdl.GL_CONTEXT_PROFILE_ES)
// Create SDL window
window, err := sdl.CreateWindow("Go SDL2 OpenGLES", sdl.WINDOWPOS_UNDEFINED, sdl.WINDOWPOS_UNDEFINED,
800, 600, sdl.WINDOW_OPENGL|sdl.WINDOW_SHOWN)
if err != nil {
panic(err)
}
defer window.Destroy()
// Create SDL OpenGL context
context, err := window.GLCreateContext()
if err != nil {
panic(err)
}
defer sdl.GLDeleteContext(context)
// Initialize GLES2
if err := gl.Init(); err != nil {
panic(err)
}
fmt.Printf("Version: %v\nRenderer: %v\n", gl.GoStr(gl.GetString(gl.VERSION)), gl.GoStr((gl.GetString(gl.RENDERER))))
fmt.Println("Press ESC to quit")
program, err := newProgram(vertexShaderSource, fragmentShaderSource)
if err != nil {
fmt.Println("Failed to create shader program:", err)
return
}
gl.UseProgram(program)
vao, vbo := makeVBO(vertices)
// Main loop
running := true
for running {
for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
switch t := event.(type) {
case *sdl.QuitEvent:
running = false
case *sdl.KeyboardEvent:
if t.Keysym.Sym == 27 {
running = false
}
}
}
// Clear the screen
gl.Clear(gl.COLOR_BUFFER_BIT)
gl.BindVertexArray(vao)
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(vertices)/3))
gl.BindVertexArray(0)
// Swap the buffers
window.GLSwap()
sdl.Delay(16) // Cap frame rate
}
// Cleanup
gl.DeleteVertexArrays(1, &vao)
gl.DeleteBuffers(1, &vbo)
gl.DeleteProgram(program)
}
func newProgram(vertexShaderSource, fragmentShaderSource string) (uint32, error) {
fmt.Printf("\nVertex script:\n%v\n", vertexShaderSource)
vertexShader, err := compileShader(vertexShaderSource, gl.VERTEX_SHADER)
if err != nil {
return 0, err
}
fmt.Printf("\nFragment script:\n%v\n", fragmentShaderSource)
fragmentShader, err := compileShader(fragmentShaderSource, gl.FRAGMENT_SHADER)
if err != nil {
return 0, err
}
program := gl.CreateProgram()
gl.AttachShader(program, vertexShader)
gl.AttachShader(program, fragmentShader)
gl.LinkProgram(program)
var status int32
gl.GetProgramiv(program, gl.LINK_STATUS, &status)
if status == gl.FALSE {
var logLength int32
gl.GetProgramiv(program, gl.INFO_LOG_LENGTH, &logLength)
log := make([]byte, logLength)
gl.GetProgramInfoLog(program, logLength, nil, &log[0])
return 0, fmt.Errorf("linking program failed: %v", string(log))
}
gl.DeleteShader(vertexShader)
gl.DeleteShader(fragmentShader)
return program, nil
}
func compileShader(source string, shaderType uint32) (uint32, error) {
shader := gl.CreateShader(shaderType)
csource, free := gl.Strs(source)
gl.ShaderSource(shader, 1, csource, 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 := make([]byte, logLength)
gl.GetShaderInfoLog(shader, logLength, nil, &log[0])
return 0, fmt.Errorf("compiling shader failed: %v", string(log))
}
return shader, nil
}
func makeVBO(vertices []float32) (uint32, uint32) {
var vbo, vao uint32
gl.GenVertexArrays(1, &vao)
gl.GenBuffers(1, &vbo)
gl.BindVertexArray(vao)
gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(vertices), gl.Ptr(vertices), gl.STATIC_DRAW)
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 3*4, nil)
gl.EnableVertexAttribArray(0)
gl.BindBuffer(gl.ARRAY_BUFFER, 0)
gl.BindVertexArray(0)
return vao, vbo
}