PlatformCore: Adjust color correction shaders

Drop the output gamma correction, as that's handled by the driver for
sRGB-encoded framebuffer.

src/platform/core/src/device/shader/color_agb.glsl.hpp

@@ -19,7 +19,6 @@ constexpr auto color_agb_frag = R"(
 
   #define darken_screen 1.0
   #define target_gamma 2.2
-  #define display_gamma 2.2
   #define sat 1.0
   #define lum 0.94
   #define contrast 1.0
@@ -48,14 +47,14 @@ constexpr auto color_agb_frag = R"(
     vec4 screen = pow(texture(u_screen_map, v_uv), vec4(target_gamma + darken_screen)).rgba;
     vec4 avglum = vec4(0.5);
     screen = mix(screen, avglum, (1.0 - contrast));
-     
+
     mat4 color = mat4(
       r,   rg,  rb,  0.0,  //red channel
       gr,  g,   gb,  0.0,  //green channel
       br,  bg,  b,   0.0,  //blue channel
       blr, blg, blb, 0.0   //alpha channel; these numbers do nothing for our purposes.
     );
-          
+
     mat4 adjust = mat4(
       (1.0 - sat) * 0.3086 + sat, (1.0 - sat) * 0.3086, (1.0 - sat) * 0.3086, 1.0,
       (1.0 - sat) * 0.6094, (1.0 - sat) * 0.6094 + sat, (1.0 - sat) * 0.6094, 1.0,
@@ -67,7 +66,6 @@ constexpr auto color_agb_frag = R"(
     screen = clamp(screen * lum, 0.0, 1.0);
     screen = color * screen;
 
-    frag_color = pow(screen, vec4(1.0 / display_gamma));
-    frag_color.a = 1;
+    frag_color = vec4(screen.rgb, 1.0);
   }
 )";

src/platform/core/src/device/shader/color_higan.glsl.hpp

@@ -20,13 +20,9 @@ constexpr auto color_higan_frag = R"(
     color.rgb = pow(color.rgb, vec3(4.0));
 
     frag_color = vec4(
-      pow(
-        vec3(
-          1.000 * color.r + 0.196 * color.g,
-          0.039 * color.r + 0.901 * color.g + 0.117 * color.b,
-          0.196 * color.r + 0.039 * color.g + 0.862 * color.b
-        ),
-        vec3(1.0 / 2.2)
-      ), 1.0);
+      1.000 * color.r + 0.196 * color.g,
+      0.039 * color.r + 0.901 * color.g + 0.117 * color.b,
+      0.196 * color.r + 0.039 * color.g + 0.862 * color.b,
+      1.0);
   }
-)";
+)";