4 bit source texture shader . for OpenGL

gistfile1.txt

#version 130
in vec2 out_uv;
out vec4 out_0;

uniform sampler2D vramimage;
uniform sampler1D vrampalette;

void main(void)
{
	vec2 uv = out_uv;
	uv.x *=0.5;	//	force read twice.
	vec4 tex = texture(vramimage, uv);	//	grab texel
	int index = int(tex.r*255.0);	//	convert the index to 0x00-0xff range
	int U = int(uv.x * 1024.0);		//	our texture is 512 so we need to double it

	if ((U&1)==1)									//	ODD pixel
		index = index & 0xf;
	else													//	EVEN pixel
		index = index>>4 & 0xf;
	out_0 = texture(vrampalette,index/255.0);
}