primera implementacio de postfx

data/shaders/postfx.vert

@@ -0,0 +1,24 @@
+#version 450
+
+// Vulkan GLSL vertex shader — postfx full-screen triangle
+// Used for SDL3 GPU API (SPIR-V path, Win/Linux).
+// Compile: glslc postfx.vert -o postfx.vert.spv
+//          xxd -i postfx.vert.spv > ../../source/core/rendering/sdl3gpu/postfx_vert_spv.h
+
+layout(location = 0) out vec2 v_uv;
+
+void main() {
+    // Full-screen triangle (no vertex buffer needed)
+    const vec2 positions[3] = vec2[3](
+        vec2(-1.0, -1.0),
+        vec2( 3.0, -1.0),
+        vec2(-1.0,  3.0)
+    );
+    const vec2 uvs[3] = vec2[3](
+        vec2(0.0, 1.0),
+        vec2(2.0, 1.0),
+        vec2(0.0,-1.0)
+    );
+    gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
+    v_uv        = uvs[gl_VertexIndex];
+}