Feature request: add sRGB internal format of texture

Internal format sRGB is same as RGB, but openGL automatically does gamma-correction when reading colors from texture. This is used in HDR rendering.

Way to add this:

code in GLTexure.uploadImageData:

Gdx.gl.glTexImage2D(target, miplevel, pixmap.getGLInternalFormat(), pixmap.getWidth(), pixmap.getHeight(), 0, pixmap.getGLFormat(), pixmap.getGLType(), pixmap.getPixels());

So, getGLInternalFormat is returned by Pixmap:

public int getGLInternalFormat () {
	return toGlFormat(format);
}

but toGlFormat never returns sRGB:

public static int toGlFormat (int format) {
	switch (format) {
	case GDX2D_FORMAT_ALPHA:
		return GL20.GL_ALPHA;
	case GDX2D_FORMAT_LUMINANCE_ALPHA:
		return GL20.GL_LUMINANCE_ALPHA;
	case GDX2D_FORMAT_RGB888:
	case GDX2D_FORMAT_RGB565:
		return GL20.GL_RGB;
	case GDX2D_FORMAT_RGBA8888:
	case GDX2D_FORMAT_RGBA4444:
		return GL20.GL_RGBA;
	default:
		throw new GdxRuntimeException("unknown format: " + format);
	}
}

As I think, one can add a few new formats or/and special flag to the Texture constructor.

P.S. Now I am achieving this by overriding Pixmap.getGLInternalFormat() method and returning something like GL30.GL_SRGB8_ALPHA8 or GL30.GL_SRGB8

Start with GLTexture.uploadImageData in gdx/src/com/badlogic/gdx/graphics/GLTexture.java and Pixmap.getGLInternalFormat and toGlFormat in Pixmap.java. Review how the Texture constructor and GL20/GL30 formats are exposed, then define a compatible way to request sRGB internal formats. Done means texture uploads can use sRGB formats without breaking the existing RGB and RGBA paths.