bgfx/examples/23-vectordisplay/fs_vectordisplay_blit.sc

$input v_color0, v_texcoord0

#include <bgfx_shader.sh>

SAMPLER2D(s_texColor,  0);

uniform vec4 u_params;
#define u_blur_scale    u_params.xy
#define u_compose_mult  u_params.z
#define u_compose_alpha u_params.w

void main()
{
	gl_FragColor = texture2D(s_texColor, v_texcoord0.xy)
				 *  vec4( u_compose_mult
						, u_compose_mult
						, u_compose_mult
						, u_compose_mult*u_compose_alpha
						);
}