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// vim: shiftwidth=4 tabstop=4 noexpandtab
package main
import (
"fmt"
"log"
"strings"
"github.com/go-gl/gl/v4.6-core/gl"
"github.com/go-gl/mathgl/mgl32"
)
var (
vertices []float32
vertex_normals []float32
)
const (
// vertex shader to draw points
VERTEX_SHADER = `
#version 410
in vec3 vp_model; // vertex position in model coordinate system
in vec3 vn_model; // vertex normal in model coordinate system
uniform mat4 trafo; // one single transformation matrix
out vec3 vn_eye; // vertex normal in eye coordinate system
void main() {
// 0.0 because translation is ignored
vn_eye = vec3(trafo * vec4(vn_model, 0.0));
gl_Position = trafo * vec4(vp_model, 1.0);
}
` + "\x00"
// fragment shader to draw surfaces
FRAGMENT_SHADER = `
#version 410
in vec3 vn_eye; // vertex normal in eye coordinate system
out vec4 frag_colour;
void main() {
vec3 ambient = vec3(0.3, 0.3, 0.3); // ambient colour is static
vec3 light_vector_eye = vec3(1.0, 0.1, -1.0);
vec3 diffuse = (vec3(1, 1, 1) - ambient) * max(dot(normalize(vn_eye),
normalize(light_vector_eye)), 0.0);
// hard-coded vector is color in RGB format:
vec3 color = (ambient + diffuse) * vec3(0, 0, 1);
frag_colour = vec4(color, 1.0); // RGBA color format
}
` + "\x00"
)
// Graphics is a struct to save OpenGL-related data like shaders.
type Graphics struct {
version string
vao uint32
vertexShader uint32
fragmentShader uint32
program uint32
trafo mgl32.Mat4
trafoUniform int32
}
// newGraphics initializes a new Graphics struct and returns it.
func newGraphics() Graphics {
var graphics Graphics = Graphics{}
graphics.trafo = mgl32.Ident4()
// init OpenGL and save/log version
log.Println("OpenGL init")
err := gl.Init()
if err != nil {
log.Fatal(err)
}
graphics.version = gl.GoStr(gl.GetString(gl.VERSION))
log.Println("OpenGL version", graphics.version)
// compile shaders
graphics.vertexShader, err = compileShader(VERTEX_SHADER, gl.VERTEX_SHADER)
if err != nil {
log.Fatal(err)
}
graphics.fragmentShader, err = compileShader(FRAGMENT_SHADER,
gl.FRAGMENT_SHADER)
if err != nil {
log.Fatal(err)
}
// create GL program
graphics.program = gl.CreateProgram()
gl.AttachShader(graphics.program, graphics.vertexShader)
gl.AttachShader(graphics.program, graphics.fragmentShader)
gl.Enable(gl.DEPTH_TEST)
gl.LinkProgram(graphics.program)
// create VAO
graphics.vao = makeVao(vertices, vertex_normals)
// create transformation matrix
gl.UniformMatrix4fv(graphics.trafoUniform, 1, false, &graphics.trafo[0])
return graphics
}
// draw executes the rendering process for a Graphics struct one time.
func (graphics Graphics) draw() {
gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
gl.UseProgram(graphics.program)
gl.UniformMatrix4fv(graphics.trafoUniform, 1, false, &graphics.trafo[0])
gl.BindVertexArray(graphics.vao)
// or alternatively POINTS, LINES, LINE_STRIP, LINE_LOOP, TRIANGLES,
// TRIANGLE_STRIP, TRIANGLE_FAN
gl.DrawArrays(gl.TRIANGLES, 0, int32(len(vertices)/3))
}
// makeVao initializes and returns a vertex array from the points provided.
func makeVao(points []float32, normals []float32) uint32 {
log.Println("Creating VAO")
// vertex buffer object (VBO) for positions:
var position_vbo uint32 // VBO ID
gl.GenBuffers(1, &position_vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, position_vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(points), gl.Ptr(points),
gl.STATIC_DRAW)
// vertex buffer object (VBO) for normals:
var normal_vbo uint32 // VBO ID
gl.GenBuffers(1, &normal_vbo)
gl.BindBuffer(gl.ARRAY_BUFFER, normal_vbo)
gl.BufferData(gl.ARRAY_BUFFER, 4*len(normals), gl.Ptr(normals),
gl.STATIC_DRAW)
// vertex array objects (VAO) to combine VBOs:
var vao uint32 // VAO ID
gl.GenVertexArrays(1, &vao)
gl.BindVertexArray(vao)
// connect position_vbo to vao
gl.BindBuffer(gl.ARRAY_BUFFER, position_vbo)
// tell GL to use 3D float vectors:
gl.VertexAttribPointer(0, 3, gl.FLOAT, false, 0, nil)
gl.EnableVertexAttribArray(0)
// connect normal_vbo to vao
gl.BindBuffer(gl.ARRAY_BUFFER, normal_vbo)
// tell GL to use 3D float vectors:
gl.VertexAttribPointer(1, 3, gl.FLOAT, false, 0, nil)
gl.EnableVertexAttribArray(1)
return vao
}
// compileShaders compiles the shader from source code.
func compileShader(source string, shaderType uint32) (uint32, error) {
log.Println("Compiling shader")
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
}
// setTrafo sets the current transformation matrix of the given Graphics struct.
func (graphics *Graphics) setTrafo(trafo mgl32.Mat4) {
graphics.trafo = trafo
}
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