diff --git a/src/Engine.Graphics.Vulkan/Shaders/triangle.frag b/src/Engine.Graphics.Vulkan/Shaders/triangle.frag
index 1a5630e..dcc2058 100644
--- a/src/Engine.Graphics.Vulkan/Shaders/triangle.frag
+++ b/src/Engine.Graphics.Vulkan/Shaders/triangle.frag
@@ -14,16 +14,11 @@ layout(set = 0, binding = 0) uniform CameraUBO {
 
 void main()
 {
-    vec3 N = normalize(fragNormal);
-    vec3 toLight = pointLightPos.xyz - fragWorldPos;
-    float dist = length(toLight);
-    vec3 L = normalize(toLight);
-
-    float NdotL = max(dot(N, L), 0.0);
-    float atten = 1.0 / (1.0 + dist * dist * 0.1);
+    // Debug: just output the light position as color
+    vec3 lp = pointLightPos.xyz;
     float intensity = pointLightPos.w;
-
-    vec3 color = fragAlbedo * pointLightColor.xyz * NdotL * intensity * atten;
-
-    outColor = vec4(color, 1.0);
+    
+    // Map position to visible range
+    vec3 debugColor = lp * 0.1 + vec3(0.5);
+    outColor = vec4(debugColor * fragAlbedo, 1.0);
 }
diff --git a/src/Engine.Graphics.Vulkan/Shaders/triangle.frag.spv b/src/Engine.Graphics.Vulkan/Shaders/triangle.frag.spv
index 78d2883..b7116fb 100644
Binary files a/src/Engine.Graphics.Vulkan/Shaders/triangle.frag.spv and b/src/Engine.Graphics.Vulkan/Shaders/triangle.frag.spv differ
diff --git a/src/Engine.Graphics.Vulkan/VulkanRenderer.cs b/src/Engine.Graphics.Vulkan/VulkanRenderer.cs
index 64db632..f340232 100644
--- a/src/Engine.Graphics.Vulkan/VulkanRenderer.cs
+++ b/src/Engine.Graphics.Vulkan/VulkanRenderer.cs
@@ -102,21 +102,13 @@ internal sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreen
 
         // Pack UBO: mat4 vp (64 bytes) + vec4 lightPos (16) + vec4 lightColor (16) = 96 bytes
         var uboData = stackalloc byte[128];
-        {
-            var vpCopy = vp;
-            var src = &vpCopy;
-            System.Buffer.MemoryCopy(src, uboData, 64, 64);
-        }
-        {
-            var lpCopy = lightPos;
-            var src = &lpCopy;
-            System.Buffer.MemoryCopy(src, uboData + 64, 16, 16);
-        }
-        {
-            var lcCopy = lightColor;
-            var src = &lcCopy;
-            System.Buffer.MemoryCopy(src, uboData + 80, 16, 16);
-        }
+        var pFloat = (float*)uboData;
+        pFloat[0] = vp.M11; pFloat[1] = vp.M12; pFloat[2] = vp.M13; pFloat[3] = vp.M14;
+        pFloat[4] = vp.M21; pFloat[5] = vp.M22; pFloat[6] = vp.M23; pFloat[7] = vp.M24;
+        pFloat[8] = vp.M31; pFloat[9] = vp.M32; pFloat[10] = vp.M33; pFloat[11] = vp.M34;
+        pFloat[12] = vp.M41; pFloat[13] = vp.M42; pFloat[14] = vp.M43; pFloat[15] = vp.M44;
+        pFloat[16] = lightPos.X; pFloat[17] = lightPos.Y; pFloat[18] = lightPos.Z; pFloat[19] = lightPos.W;
+        pFloat[20] = lightColor.X; pFloat[21] = lightColor.Y; pFloat[22] = lightColor.Z; pFloat[23] = lightColor.W;
 
         var drawCalls = new List<(VkBuffer vertexBuf, VkBuffer indexBuf, uint indexCount, Matrix4x4 model)>();