Porta tots els shaders a Vulkan i Metal

shaders/_common/passthrough.vk.glsl

@@ -2,7 +2,6 @@
 
 // Shared fullscreen-triangle vertex shader for the SDL3 GPU backend.
 // Emits vUV in Shadertoy convention: (0,0) bottom-left, (1,1) top-right.
-// Y flipped in NDC because Vulkan/Metal point Y down by default.
 
 layout(location = 0) out vec2 vUV;
 
@@ -14,5 +13,5 @@ void main() {
     );
     vec2 pos = positions[gl_VertexIndex];
     vUV = pos * 0.5 + 0.5;
-    gl_Position = vec4(pos.x, -pos.y, 0.0, 1.0);
+    gl_Position = vec4(pos, 0.0, 1.0);
 }