gl: add internalFormat to TexImage2D

The OpenGL C function glTexImage2D has the following signature:

void glTexImage2D(GLenum target,
 	GLint level,
 	GLint internalFormat,
 	GLsizei width,
 	GLsizei height,
 	GLint border,
 	GLenum format,
 	GLenum type,
 	const GLvoid * data);

However, the corresponding Context.TexImage2D method in package gl
does not include the internalFormat parameter, and use the format
argument instead. That's ok for many texture formats; for example,
RGBA textures have both format and internalFormat set to GL_RGBA.
But not always. In particular, OpenGL ES 3 allows the use of sRGB
encoded textures by specifying GL_SRGB8_ALPHA8 as internalFormat,
but keeping GL_RGBA as format.

Add the internalFormat to the Context package. This is unfortunately
a breaking change, but adding a new function ("glTexImage2D2"?) to
Context is too ugly for a parameter that should have been there all
along. (Adding a new method to the Context interface is technically
also a breaking change, but I don't expect that there are any
external implementers of the interface).

Change-Id: I12a45a34f604e51cb1be26aed906025ccfac533a
Reviewed-on: https://go-review.googlesource.com/133155
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>

Author: Elias Naur

exp/gl/glutil/glimage.go

@@ -124,7 +124,7 @@ func (p *Images) NewImage(w, h int) *Image {
 	img.gltex = p.glctx.CreateTexture()
 
 	p.glctx.BindTexture(gl.TEXTURE_2D, img.gltex)
-	p.glctx.TexImage2D(gl.TEXTURE_2D, 0, img.width, img.height, gl.RGBA, gl.UNSIGNED_BYTE, nil)
+	p.glctx.TexImage2D(gl.TEXTURE_2D, 0, gl.RGBA, img.width, img.height, gl.RGBA, gl.UNSIGNED_BYTE, nil)
 	p.glctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR)
 	p.glctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR)
 	p.glctx.TexParameteri(gl.TEXTURE_2D, gl.TEXTURE_WRAP_S, gl.CLAMP_TO_EDGE)

gl/gl.go

@@ -1257,7 +1257,7 @@ func (ctx *context) StencilOpSeparate(face, sfail, dpfail, dppass Enum) {
 	})
 }
 
-func (ctx *context) TexImage2D(target Enum, level int, width, height int, format Enum, ty Enum, data []byte) {
+func (ctx *context) TexImage2D(target Enum, level int, internalFormat int, width, height int, format Enum, ty Enum, data []byte) {
 	// It is common to pass TexImage2D a nil data, indicating that a
 	// bound GL buffer is being used as the source. In that case, it
 	// is not necessary to block.
@@ -1272,7 +1272,7 @@ func (ctx *context) TexImage2D(target Enum, level int, width, height int, format
 			// TODO(crawshaw): GLES3 offset for PIXEL_UNPACK_BUFFER and PIXEL_PACK_BUFFER.
 			a0: target.c(),
 			a1: uintptr(level),
-			a2: uintptr(format),
+			a2: uintptr(internalFormat),
 			a3: uintptr(width),
 			a4: uintptr(height),
 			a5: format.c(),

gl/gldebug.go

@@ -627,7 +627,7 @@ type Context interface {
 	// TexImage2D writes a 2D texture image.
 	//
 	// http://www.khronos.org/opengles/sdk/docs/man3/html/glTexImage2D.xhtml
-	TexImage2D(target Enum, level int, width, height int, format Enum, ty Enum, data []byte)
+	TexImage2D(target Enum, level int, internalFormat int, width, height int, format Enum, ty Enum, data []byte)
 
 	// TexSubImage2D writes a subregion of a 2D texture image.
 	//