Simple OpenGL 2D drawing

main.go

package main

import (
	"fmt"
	"strings"
	gl "github.com/chsc/gogl/gl42"
	glfw "github.com/go-gl/glfw"
	glutil "github.com/go3d/go-util/gl"
)

type tGeometry struct {
	glVerts []gl.Float
	glNumVerts gl.Sizei
	glMode gl.Enum
	glVertBuf gl.Uint
}

var (
	faceTri, faceQuad = &tGeometry {}, &tGeometry {}
	useStrictCoreProfile = false // set this to true to see the problem...
	isFirstLoop = true // only output glLastError in the loop's first iteration
	lastErr error
	shaderProg *glutil.TShaderProgram
	srcVertShader = "in vec3 aPos; void main () { gl_Position = vec4(aPos, 1.0); }"
	srcFragShader = "out vec4 oColor; void main () { oColor = vec4(0.0, 0.6, 0.9, 1.0); }"
)

func compileShaders () (err error) {
	var glStatus gl.Int
	var glFrag = gl.CreateShader(gl.FRAGMENT_SHADER)
	var glVert = gl.CreateShader(gl.VERTEX_SHADER)
	glutil.ShaderSource("test", glFrag, srcFragShader, nil, false, "150")
	gl.CompileShader(glFrag)
	if gl.GetShaderiv(glFrag, gl.COMPILE_STATUS, &glStatus); glStatus == 0 {
		err = fmt.Errorf("SHADER %s: %s\n", "Frag", glutil.ShaderInfoLog(glFrag, true)); return
	}
	glutil.ShaderSource("test", glVert, srcVertShader, nil, false, "150")
	gl.CompileShader(glVert)
	if gl.GetShaderiv(glVert, gl.COMPILE_STATUS, &glStatus); glStatus == 0 {
		err = fmt.Errorf("SHADER %s: %s\n", "Vert", glutil.ShaderInfoLog(glVert, true)); return
	}
	if shaderProg, err = glutil.NewShaderProgram("test", 0, glFrag, 0, 0, 0, glVert); err == nil {
		err = shaderProg.SetAttrLocations("aPos")
	}
	return
}

func deleteGeometry () {
	gl.DeleteBuffers(1, &faceTri.glVertBuf)
	gl.DeleteBuffers(1, &faceQuad.glVertBuf)
}

func renderGeometry (mesh *tGeometry) {
	gl.BindBuffer(gl.ARRAY_BUFFER, mesh.glVertBuf)
if isFirstLoop { logLastGlError("render.BindBuffer(buf)") }

	gl.VertexAttribPointer(shaderProg.AttrLocs["aPos"], 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil))
if isFirstLoop { logLastGlError("render.VertexAttribPointer()") }

	gl.DrawArrays(mesh.glMode, 0, mesh.glNumVerts)
if isFirstLoop { logLastGlError("render.DrawArrays()") }

	gl.BindBuffer(gl.ARRAY_BUFFER, 0)
if isFirstLoop { logLastGlError("render.BindBuffer(0)") }
}

func setupGeometry () {
	var z gl.Float = -1
	faceTri.glMode, faceTri.glNumVerts, faceTri.glVerts = gl.TRIANGLES, 3, []gl.Float {
		0, 1, z,
		-1, -1, z,
		1, -1, z,
	}
	uploadGeometry(faceTri)
	faceQuad.glMode, faceQuad.glNumVerts, faceQuad.glVerts = gl.TRIANGLE_STRIP, 4, []gl.Float {
		0.5, 0.5, z,
		-0.5, 0.5, z,
		0.5, -0.5, z,
		-0.5, -0.5, z,
	}
	uploadGeometry(faceQuad)
}

func uploadGeometry (mesh *tGeometry) {
	gl.GenBuffers(1, &mesh.glVertBuf)
	gl.BindBuffer(gl.ARRAY_BUFFER, mesh.glVertBuf)
	gl.BufferData(gl.ARRAY_BUFFER, gl.Sizeiptr(4 * len(mesh.glVerts)), gl.Pointer(&mesh.glVerts[0]), gl.STATIC_DRAW)
	gl.BindBuffer(gl.ARRAY_BUFFER, 0)
}

func logLastGlError (step string) {
	if lastErr = glutil.LastError(step); lastErr != nil { fmt.Printf("LASTERR: %v\n", lastErr) }
}

func main () {
	var err error
	var looping = true
	defer fmt.Println("EXIT")
	if err = glfw.Init(); err != nil { panic(err) }
	defer glfw.Terminate()
	glfw.OpenWindowHint(glfw.FsaaSamples, 0)
	if useStrictCoreProfile {
		glfw.OpenWindowHint(glfw.OpenGLVersionMajor, 3)
		glfw.OpenWindowHint(glfw.OpenGLVersionMinor, 2)
		glfw.OpenWindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
	//	if runtime.GOOS == "darwin" { glfw.OpenWindowHint(glfw.OpenGLForwardCompat, 1) }
	}

	if err = glfw.OpenWindow(1280, 720, 8, 8, 8, 0, 24, 8, glfw.Windowed); err != nil { panic(err) }
	defer glfw.CloseWindow()
	glfw.Enable(glfw.StickyKeys)
	if err = gl.Init(); (err != nil) && (strings.Index(err.Error(), "VERSION_") < 0) { panic(err) }
	defer logLastGlError("(post loop)")
	glutil.SetVersion()
	fmt.Printf("GLCONN: %v\n", glutil.GlConnInfo())
	gl.ClearColor(0.3, 0.1, 0.0, 1.0)
	gl.Enable(gl.DEPTH_TEST)
	gl.FrontFace(gl.CCW)
	gl.CullFace(gl.BACK)
	gl.Disable(gl.CULL_FACE)
	if err = compileShaders(); err != nil { panic(err) }
	setupGeometry()
	logLastGlError("(pre loop)")

	for looping {
		gl.UseProgram(shaderProg.Program)
if isFirstLoop { logLastGlError("gl.UseProgram") }

		gl.Viewport(0, 0, 1280, 720)
if isFirstLoop { logLastGlError("gl.ViewPort") }

		gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
if isFirstLoop { logLastGlError("gl.Clear") }

		renderGeometry(faceTri)
		renderGeometry(faceQuad)
		if (glfw.WindowParam(glfw.Opened) != 1) || (glfw.Key(glfw.KeyEsc) == glfw.KeyPress) {
			looping = false
		} else {
			glfw.SwapBuffers()
		}
		isFirstLoop = false
	}

}

Note, you won't find a glEnableVertexAttribArray call in the above Gist, as it's inside the glutil package I'm importing -- but this does get called as the last step in this Gist's compileShaders() func.