fix: move light data from UBO to push constants — fixes std140 layout issue

Root cause: GLSL std140 layout adds padding after mat4 for vec4 fields,
causing light data to be read at wrong offsets → NaN/artifacts.

Fix:
- UBO back to 64 bytes (mat4 vp only)
- Light data (pos + color, 32 bytes) sent via push constants at offset 64
- Two push constant ranges: Vertex (0-64, model) + Fragment (64-96, light)
- Both vertex and fragment shaders read from same push_constant block
- PBR shader fully restored with Cook-Torrance BRDF
- Dynamic point light follows physics ball

src/Engine.Graphics.Vulkan/Shaders/triangle.frag

@@ -10,22 +10,97 @@ layout(set = 0, binding = 0) uniform CameraUBO {
     mat4 vp;
 };
 
+layout(push_constant) uniform PC {
+    mat4 model;
+    vec4 lightPos;
+    vec4 lightColor;
+} pc;
+
+const vec3 AMBIENT = vec3(0.01, 0.01, 0.02);
+const float PI = 3.14159265359;
+
+float distributionGGX(vec3 N, vec3 H, float roughness)
+{
+    float a = roughness * roughness;
+    float a2 = a * a;
+    float NdotH = max(dot(N, H), 0.0);
+    float NdotH2 = NdotH * NdotH;
+    float num = a2;
+    float denom = NdotH2 * (a2 - 1.0) + 1.0;
+    denom = PI * denom * denom;
+    return num / denom;
+}
+
+float geometrySchlickGGX(float NdotV, float roughness)
+{
+    float r = roughness + 1.0;
+    float k = (r * r) / 8.0;
+    return NdotV / (NdotV * (1.0 - k) + k);
+}
+
+float geometrySmith(vec3 N, vec3 V, vec3 L, float roughness)
+{
+    float NdotV = max(dot(N, V), 0.0);
+    float NdotL = max(dot(N, L), 0.0);
+    return geometrySchlickGGX(NdotV, roughness) * geometrySchlickGGX(NdotL, roughness);
+}
+
+vec3 fresnelSchlick(float cosTheta, vec3 F0)
+{
+    return F0 + (1.0 - F0) * pow(clamp(1.0 - cosTheta, 0.0, 1.0), 5.0);
+}
+
+vec3 acesTonemap(vec3 color)
+{
+    float a = 2.51;
+    float b = 0.03;
+    float c = 2.43;
+    float d = 0.59;
+    float e = 0.14;
+    return clamp((color * (a * color + b)) / (color * (c * color + d) + e), 0.0, 1.0);
+}
+
 void main()
 {
     vec3 N = normalize(fragNormal);
-    
-    // Hardcoded light at (0, 10, 0) — test if lighting works at all
-    vec3 lightPos = vec3(0.0, 10.0, 0.0);
+    vec3 V = normalize(-fragWorldPos);
+    vec3 albedo = fragAlbedo;
+    float roughness = 0.5;
+    float metallic = 0.1;
+
+    vec3 color = AMBIENT * albedo;
+
+    vec3 lightPos = pc.lightPos.xyz;
+    float lightIntensity = pc.lightPos.w;
+    vec3 lightColor = pc.lightColor.xyz;
+    float lightRange = pc.lightColor.w;
+
     vec3 toLight = lightPos - fragWorldPos;
     float dist = length(toLight);
-    vec3 L = normalize(toLight);
+    vec3 L = toLight / max(dist, 0.001);
+
+    float attenuation = pow(clamp(1.0 - dist / max(lightRange, 0.001), 0.0, 1.0), 2.0);
+    vec3 radiance = lightColor * lightIntensity * attenuation;
+
+    vec3 H = normalize(V + L);
+    vec3 F0 = mix(vec3(0.04), albedo, metallic);
+
+    float NDF = distributionGGX(N, H, roughness);
+    float G = geometrySmith(N, V, L, roughness);
+    vec3 F = fresnelSchlick(max(dot(H, V), 0.0), F0);
+
+    vec3 numerator = NDF * G * F;
+    float denominator = 4.0 * max(dot(N, V), 0.0) * max(dot(N, L), 0.0) + 0.0001;
+    vec3 specular = numerator / denominator;
+
+    vec3 kS = F;
+    vec3 kD = (vec3(1.0) - kS) * (1.0 - metallic);
 
     float NdotL = max(dot(N, L), 0.0);
-    float atten = 1.0 / (1.0 + dist * dist * 0.05);
-    float intensity = 30.0;
+    color += (kD * albedo / PI + specular) * radiance * NdotL;
 
-    vec3 color = fragAlbedo * vec3(1.0, 0.9, 0.7) * NdotL * intensity * atten;
-    color += fragAlbedo * 0.02;
+    color = acesTonemap(color);
+    color = pow(color, vec3(1.0 / 2.2));
 
     outColor = vec4(color, 1.0);
 }

src/Engine.Graphics.Vulkan/Shaders/triangle.vert

@@ -10,16 +10,17 @@ layout(location = 2) out vec3 fragAlbedo;
 
 layout(set = 0, binding = 0) uniform CameraUBO {
     mat4 vp;
-    vec4 pointLightPos;     // xyz = position, w = intensity
-    vec4 pointLightColor;   // xyz = color, w = range
 };
 
 layout(push_constant) uniform PC {
     mat4 model;
+    vec4 lightPos;
+    vec4 lightColor;
 } pc;
 
 void main() {
     vec4 worldPos = pc.model * vec4(inPosition, 1.0);
+    gl_Position = pc.model * vec4(inPosition, 1.0);
     gl_Position = vp * worldPos;
     fragWorldPos = worldPos.xyz;
     fragNormal = mat3(pc.model) * inNormal;

src/Engine.Graphics.Vulkan/VulkanFrameResources.cs

@@ -5,7 +5,7 @@ namespace Engine.Graphics.Vulkan;
 internal sealed unsafe class VulkanFrameResources : IDisposable
 {
     public const int MaxFramesInFlight = 2;
-    public const ulong UboSize = 128;
+    public const ulong UboSize = 64;
 
     public VkCommandPool CommandPool;
     public VkCommandBuffer[] CommandBuffers = new VkCommandBuffer[MaxFramesInFlight];

src/Engine.Graphics.Vulkan/VulkanPipeline.cs

@@ -150,12 +150,19 @@ internal sealed unsafe class VulkanPipeline : IDisposable
                 pDynamicStates = dynamicStates,
             };
 
-            var pushConstantRange = new VkPushConstantRange
+            var pushConstantRanges = stackalloc VkPushConstantRange[2];
+            pushConstantRanges[0] = new VkPushConstantRange
             {
-            stageFlags = VkShaderStageFlags.Vertex | VkShaderStageFlags.Fragment,
+                stageFlags = VkShaderStageFlags.Vertex,
                 offset = 0,
                 size = 64,
             };
+            pushConstantRanges[1] = new VkPushConstantRange
+            {
+                stageFlags = VkShaderStageFlags.Fragment,
+                offset = 64,
+                size = 32,
+            };
 
             var descLayout = DescriptorSetLayout;
             var layoutInfo = new VkPipelineLayoutCreateInfo
@@ -163,8 +170,8 @@ internal sealed unsafe class VulkanPipeline : IDisposable
                 sType = VkStructureType.PipelineLayoutCreateInfo,
                 setLayoutCount = 1,
                 pSetLayouts = &descLayout,
-                pushConstantRangeCount = 1,
-                pPushConstantRanges = (nint)(&pushConstantRange),
+                pushConstantRangeCount = 2,
+                pPushConstantRanges = (nint)pushConstantRanges,
             };
 
             fixed (VkPipelineLayout* layoutPtr = &PipelineLayout)

src/Engine.Graphics.Vulkan/VulkanRenderer.cs

@@ -100,14 +100,10 @@ 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];
+        // Pack UBO: just mat4 vp (64 bytes)
+        var uboData = stackalloc byte[64];
         var vpCopy = vp;
         System.Buffer.MemoryCopy(&vpCopy, uboData, 64, 64);
-        var lpCopy = lightPos;
-        System.Buffer.MemoryCopy(&lpCopy, uboData + 64, 16, 16);
-        var lcCopy = lightColor;
-        System.Buffer.MemoryCopy(&lcCopy, uboData + 80, 16, 16);
 
         var drawCalls = new List<(VkBuffer vertexBuf, VkBuffer indexBuf, uint indexCount, Matrix4x4 model)>();
 
@@ -127,10 +123,10 @@ internal sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreen
             drawCalls.Add((entry.vb.Buffer, entry.ib.Buffer, entry.indexCount, t.GetMatrix()));
         });
 
-        Render(vp, drawCalls, uboData);
+        Render(vp, drawCalls, uboData, lightPos, lightColor);
     }
 
-    private void Render(Matrix4x4 vp, List<(VkBuffer vertexBuf, VkBuffer indexBuf, uint indexCount, Matrix4x4 model)> drawCalls, byte* uboData)
+    private void Render(Matrix4x4 vp, List<(VkBuffer vertexBuf, VkBuffer indexBuf, uint indexCount, Matrix4x4 model)> drawCalls, byte* uboData, Vector4 lightPos, Vector4 lightColor)
     {
         _frameResources.WaitFrame(_frameIndex);
 
@@ -142,7 +138,7 @@ internal sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreen
         {
             _swapchain.Recreate(_ctx.SurfaceExtent.Width == 0 ? 1280 : (int)_ctx.SurfaceExtent.Width,
                                 _ctx.SurfaceExtent.Height == 0 ? 720 : (int)_ctx.SurfaceExtent.Height);
-            Render(vp, drawCalls, uboData);
+            Render(vp, drawCalls, uboData, lightPos, lightColor);
             return;
         }
 
@@ -250,6 +246,13 @@ internal sealed unsafe class VulkanRenderer : IRenderer, Engine.Graphics.IScreen
 
             var model = dc.model;
             Vk.vkCmdPushConstants(cmd, _pipeline.PipelineLayout, VkShaderStageFlags.Vertex, 0, 64, &model);
+
+            // Light data as push constants at offset 64 (fragment stage)
+            var lpCopy = lightPos;
+            Vk.vkCmdPushConstants(cmd, _pipeline.PipelineLayout, VkShaderStageFlags.Fragment, 64, 16, &lpCopy);
+            var lcCopy = lightColor;
+            Vk.vkCmdPushConstants(cmd, _pipeline.PipelineLayout, VkShaderStageFlags.Fragment, 80, 16, &lcCopy);
+
             Vk.vkCmdDrawIndexed(cmd, dc.indexCount, 1, 0, 0, 0);
         }