uniform sampler2D tex;

uniform sampler2D videoTex;

uniform vec4 cnst;

uniform vec3 texStepX; // = vec3(vec2(1.0 / texSize.x), 0.0);

varying vec2 scaled;

varying vec3 misc;

varying vec2 videoCoord;

void main()

{

	float scan_a = cnst.x;

	float scan_b = cnst.y;

	float scan_c = cnst.z;

	float alpha  = cnst.w;

	vec3 t = (vec3(floor(scaled.x)) + alpha * vec3(fract(scaled.x))) * texStepX + misc;

	vec4 col1 = texture2D(tex, t.xz);

	vec4 col2 = texture2D(tex, t.yz);

	float scan = scan_c + scan_b * abs(fract(scaled.y) - scan_a);

#if SUPERIMPOSE

	vec4 col = (col1 + col2) / 2.0;

	vec4 vid = texture2D(videoTex, videoCoord);

	gl_FragColor = mix(vid, col, col.a) * scan;

#else

	// optimization: in case of not-superimpose, we moved the division by 2

	// '(col1 + col2) / 2' to the 'scan_b' and 'scan_c' variables.

	gl_FragColor = (col1 + col2) * scan;

#endif

}