libobs: Add premultiplied alpha base effect

libobs/data/premultiplied_alpha.effect

@@ -0,0 +1,38 @@
+uniform float4x4 ViewProj;
+uniform texture2d image;
+
+sampler_state def_sampler {
+	Filter   = Linear;
+	AddressU = Clamp;
+	AddressV = Clamp;
+};
+
+struct VertInOut {
+	float4 pos : POSITION;
+	float2 uv  : TEXCOORD0;
+};
+
+VertInOut VSDefault(VertInOut vert_in)
+{
+	VertInOut vert_out;
+	vert_out.pos = mul(float4(vert_in.pos.xyz, 1.0), ViewProj);
+	vert_out.uv  = vert_in.uv;
+	return vert_out;
+}
+
+float4 PSDraw(VertInOut vert_in) : TARGET
+{
+	float4 rgba = image.Sample(def_sampler, vert_in.uv);
+	if (rgba.a > 0.0)
+		rgba.rgb /= rgba.a;
+	return saturate(rgba);
+}
+
+technique Draw
+{
+	pass
+	{
+		vertex_shader = VSDefault(vert_in);
+		pixel_shader  = PSDraw(vert_in);
+	}
+}

libobs/obs-internal.h

@@ -237,6 +237,7 @@ struct obs_core_video {
 	gs_effect_t                     *bicubic_effect;
 	gs_effect_t                     *lanczos_effect;
 	gs_effect_t                     *bilinear_lowres_effect;
+	gs_effect_t                     *premultiplied_alpha_effect;
 	gs_stagesurf_t                  *mapped_surface;
 	int                             cur_texture;
 

libobs/obs.c

@@ -291,6 +291,11 @@ static int obs_init_graphics(struct obs_video_info *ovi)
 			NULL);
 	bfree(filename);
 
+	filename = find_libobs_data_file("premultiplied_alpha.effect");
+	video->premultiplied_alpha_effect = gs_effect_create_from_file(filename,
+			NULL);
+	bfree(filename);
+
 	obs->video.transparent_texture = gs_texture_create(2, 2, GS_RGBA, 1,
 			&transparent_tex, 0);
 
@@ -306,6 +311,8 @@ static int obs_init_graphics(struct obs_video_info *ovi)
 		success = false;
 	if (!video->conversion_effect)
 		success = false;
+	if (!video->premultiplied_alpha_effect)
+		success = false;
 	if (!video->transparent_texture)
 		success = false;
 
@@ -1351,6 +1358,8 @@ gs_effect_t *obs_get_base_effect(enum obs_base_effect effect)
 		return obs->video.lanczos_effect;
 	case OBS_EFFECT_BILINEAR_LOWRES:
 		return obs->video.bilinear_lowres_effect;
+	case OBS_EFFECT_PREMULTIPLIED_ALPHA:
+		return obs->video.premultiplied_alpha_effect;
 	}
 
 	return NULL;

libobs/obs.h

@@ -521,6 +521,7 @@ enum obs_base_effect {
 	OBS_EFFECT_BICUBIC,            /**< Bicubic downscale */
 	OBS_EFFECT_LANCZOS,            /**< Lanczos downscale */
 	OBS_EFFECT_BILINEAR_LOWRES,    /**< Bilinear low resolution downscale */
+	OBS_EFFECT_PREMULTIPLIED_ALPHA,/**< Premultiplied alpha */
 };
 
 /** Returns a commonly used base effect */