macos fix

1 files changed, 20 insertions, 7 deletions

diff --git a/shaders/crt.frag.glsl b/shaders/crt.frag.glsl
index e43d5b86..b0b0b93b 100644
--- a/shaders/crt.frag.glsl
+++ b/shaders/crt.frag.glsl
@@ -81,24 +81,29 @@ vec2 sceneUv(vec2 uv) {
     return uv;
 }
 
-vec3 sceneSrgb(vec2 uv) {
+// The scene, ALPHA INCLUDED: with a see-through ground the grid arrives
+// premultiplied and partly empty, and a pass that dropped .a would turn the
+// desktop behind a `*_transparent` theme into opaque black the moment Crt,
+// Ripple or Glitch came on.
+vec4 sceneSrgb(vec2 uv) {
     vec2 warped = sceneUv(uv);
-    vec3 center = texture(u_scene, warped).rgb;
+    vec4 center = texture(u_scene, warped);
     if (u_crt.effects.z <= 0.5) return center;
 
     float band = floor(warped.y * 96.0);
     float seed = noiseAt(vec2(band, floor(u_crt.time_seconds * 13.0)));
     float tear = smoothstep(0.955, 1.0, seed);
     vec2 chroma = vec2((0.35 + 1.25 * tear) / u_crt.viewport.x, 0.0);
-    return vec3(
+    return vec4(
         texture(u_scene, warped + chroma).r,
         center.g,
-        texture(u_scene, warped - chroma).b
+        texture(u_scene, warped - chroma).b,
+        center.a
     );
 }
 
 vec3 effectSceneLinear(vec2 uv) {
-    return srgbToLinear(sceneSrgb(uv));
+    return srgbToLinear(sceneSrgb(uv).rgb);
 }
 
 void main() {
@@ -113,11 +118,16 @@ void main() {
     if (u_crt.effects.x <= 0.5) {
         // The scene texture is already sRGB. Avoid a needless transfer-curve
         // round trip so a coordinate-only effect preserves theme bytes.
-        o_col = vec4(clamp(sceneSrgb(uv), 0.0, 1.0), 1.0);
+        vec4 s = sceneSrgb(uv);
+        o_col = vec4(clamp(s.rgb, 0.0, 1.0), clamp(s.a, 0.0, 1.0));
         return;
     }
 
     vec3 col = vec3(0.0);
+    // Outside the tube nothing is drawn, so nothing is covered either: the
+    // old opaque black there would have punched a rectangle out of the
+    // compositor's backdrop.
+    float alpha = 0.0;
     float edge = min(min(uv.x, uv.y), min(1.0 - uv.x, 1.0 - uv.y));
     if (edge > 0.0) {
         vec3 center = effectSceneLinear(uv);
@@ -153,10 +163,13 @@ void main() {
         float vignette = 1.0 - VIGNETTE_STRENGTH * pow(clamp(r2 * 0.5, 0.0, 1.0), 1.6);
         float hum = 1.0 + HUM_STRENGTH * sin((uv.y * 1.35 - u_crt.time_seconds * 0.11) * TAU);
         col *= tube * vignette * hum * EXPOSURE;
+        // The tube's edge falloff dims coverage as well as colour; everything
+        // else here is a light adjustment and leaves it alone.
+        alpha = sceneSrgb(uv).a * tube;
 
         float luma = dot(col, vec3(0.2126, 0.7152, 0.0722));
         vec2 noise_seed = gl_FragCoord.xy + vec2(u_crt.frame * 17.0, u_crt.frame * 59.0);
         col += (noiseAt(noise_seed) - 0.5) * NOISE_STRENGTH * (0.15 + 0.85 * clamp(luma, 0.0, 1.0));
     }
-    o_col = vec4(linearToSrgb(clamp(col, 0.0, 1.0)), 1.0);
+    o_col = vec4(linearToSrgb(clamp(col, 0.0, 1.0)), clamp(alpha, 0.0, 1.0));
 }