go.mobile/gl/glutil: OpenGL utilities package

No tests yet. I am working on a gltest package that can
create a windowless context on a variety of platforms for
testing GL code, but given current priorities it is a
couple of weeks away.

LGTM=nigeltao
R=nigeltao
CC=golang-codereviews
https://golang.org/cl/135450043

gl/glutil/glutil.go

@@ -0,0 +1,58 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package glutil implements OpenGL utility functions.
+package glutil
+
+import (
+	"fmt"
+
+	"code.google.com/p/go.mobile/gl"
+)
+
+// CreateProgram creates, compiles, and links a gl.Program.
+func CreateProgram(vertexSrc, fragmentSrc string) (gl.Program, error) {
+	program := gl.CreateProgram()
+	if program == 0 {
+		return 0, fmt.Errorf("glutil: no programs available")
+	}
+
+	vertexShader, err := loadShader(gl.VERTEX_SHADER, vertexSrc)
+	if err != nil {
+		return 0, err
+	}
+	fragmentShader, err := loadShader(gl.FRAGMENT_SHADER, fragmentSrc)
+	if err != nil {
+		gl.DeleteShader(vertexShader)
+		return 0, err
+	}
+
+	gl.AttachShader(program, vertexShader)
+	gl.AttachShader(program, fragmentShader)
+	gl.LinkProgram(program)
+
+	// Flag shaders for deletion when program is unlinked.
+	gl.DeleteShader(vertexShader)
+	gl.DeleteShader(fragmentShader)
+
+	if gl.GetProgrami(program, gl.LINK_STATUS) == 0 {
+		defer gl.DeleteProgram(program)
+		return 0, fmt.Errorf("glutil: %s", gl.GetProgramInfoLog(program))
+	}
+	return program, nil
+}
+
+func loadShader(shaderType gl.Enum, src string) (gl.Shader, error) {
+	shader := gl.CreateShader(shaderType)
+	if shader == 0 {
+		return 0, fmt.Errorf("glutil: could not create shader (type %v)", shaderType)
+	}
+	gl.ShaderSource(shader, src)
+	gl.CompileShader(shader)
+	if gl.GetShaderi(shader, gl.COMPILE_STATUS) == 0 {
+		defer gl.DeleteShader(shader)
+		return 0, fmt.Errorf("shader compile: %s", gl.GetShaderInfoLog(shader))
+	}
+	return shader, nil
+}