[vertex]


layout(location=0) in highp vec4 vertex_attrib;


void main() {

	gl_Position = vertex_attrib;

}

[fragment]


uniform highp sampler2D source_exposure; //texunit:0

#ifdef EXPOSURE_BEGIN

uniform highp ivec2 source_render_size;
uniform highp ivec2 target_size;

#endif

#ifdef EXPOSURE_END

uniform highp sampler2D prev_exposure; //texunit:1
uniform highp float exposure_adjust;
uniform highp float min_luminance;
uniform highp float max_luminance;

#endif

layout(location = 0) out highp float exposure;



void main() {



#ifdef EXPOSURE_BEGIN


	ivec2 src_pos = ivec2(gl_FragCoord.xy)*source_render_size/target_size;

#if 1
	//more precise and expensive, but less jittery
	ivec2 next_pos = ivec2(gl_FragCoord.xy+ivec2(1))*source_render_size/target_size;
	next_pos = max(next_pos,src_pos+ivec2(1)); //so it at least reads one pixel
	highp vec3 source_color=vec3(0.0);
	for(int i=src_pos.x;i<next_pos.x;i++) {
		for(int j=src_pos.y;j<next_pos.y;j++) {
			source_color += texelFetch(source_exposure,ivec2(i,j),0).rgb;
		}
	}

	source_color/=float( (next_pos.x-src_pos.x)*(next_pos.y-src_pos.y) );
#else
	highp vec3 source_color = texelFetch(source_exposure,src_pos,0).rgb;

#endif

	exposure = max(source_color.r,max(source_color.g,source_color.b));

#else

	ivec2 coord = ivec2(gl_FragCoord.xy);
	exposure  = texelFetch(source_exposure,coord*3+ivec2(0,0),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(1,0),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(2,0),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(0,1),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(1,1),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(2,1),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(0,2),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(1,2),0).r;
	exposure += texelFetch(source_exposure,coord*3+ivec2(2,2),0).r;
	exposure *= (1.0/9.0);

#ifdef EXPOSURE_END

#ifdef EXPOSURE_FORCE_SET
	//will stay as is
#else
	highp float prev_lum = texelFetch(prev_exposure,ivec2(0,0),0).r; //1 pixel previous exposure
	exposure = clamp( prev_lum + (exposure-prev_lum)*exposure_adjust,min_luminance,max_luminance);

#endif //EXPOSURE_FORCE_SET


#endif //EXPOSURE_END

#endif //EXPOSURE_BEGIN


}