obs-transitions: Nonlinear SRGB, fade to color

Switch back for now. Maybe we want CIELUV, but that's expensive.

plugins/obs-transitions/data/fade_to_color_transition.effect

@@ -24,7 +24,8 @@ VertData VSDefault(VertData v_in)
 
 float4 PSFadeToColor(VertData v_in) : TARGET
 {
-	return lerp(tex.Sample(textureSampler, v_in.uv), color, swp);
+	float4 premultiplied = float4(color.rgb * color.a, color.a);
+	return lerp(tex.Sample(textureSampler, v_in.uv), premultiplied, swp);
 }
 
 technique FadeToColor

plugins/obs-transitions/transition-fade-to-color.c

@@ -52,7 +52,7 @@ static void fade_to_color_update(void *data, obs_data_t *settings)
 
 	color |= 0xFF000000;
 
-	vec4_from_rgba_srgb_premultiply(&fade_to_color->color, color);
+	vec4_from_rgba(&fade_to_color->color, color);
 
 	fade_to_color->switch_point = (float)swp / 100.0f;
 }
@@ -105,19 +105,13 @@ static void fade_to_color_callback(void *data, gs_texture_t *a, gs_texture_t *b,
 
 	float swp = t < fade_to_color->switch_point ? sa : 1.0f - sb;
 
-	gs_texture_t *const tex = (t < fade_to_color->switch_point) ? a : b;
-
-	const bool previous = gs_framebuffer_srgb_enabled();
-	gs_enable_framebuffer_srgb(true);
-
-	gs_effect_set_texture_srgb(fade_to_color->ep_tex, tex);
-	gs_effect_set_vec4(fade_to_color->ep_color, &fade_to_color->color);
+	gs_effect_set_texture(fade_to_color->ep_tex,
+			      t < fade_to_color->switch_point ? a : b);
 	gs_effect_set_float(fade_to_color->ep_swp, swp);
+	gs_effect_set_vec4(fade_to_color->ep_color, &fade_to_color->color);
 
 	while (gs_effect_loop(fade_to_color->effect, "FadeToColor"))
 		gs_draw_sprite(NULL, 0, cx, cy);
-
-	gs_enable_framebuffer_srgb(previous);
 }
 
 static void fade_to_color_video_render(void *data, gs_effect_t *effect)