use shader uniforms for scaling cube

Sources/Voxelotl/Renderer.swift

@@ -218,6 +218,10 @@ class Renderer {
   }
 
   func paint() throws {
+    var uniforms = ShaderUniforms(
+      model: .init(diagonal: .init(0.5, 0.5, 0.5, 1.0)),
+      projView: matrix_identity_float4x4)
+
     guard let rt = layer.nextDrawable() else {
       throw RendererError.drawFailure("Failed to get next drawable render target")
     }
@@ -239,6 +243,10 @@ class Renderer {
     encoder.setVertexBuffer(vtxBuffer,
       offset: 0,
       index: ShaderInputIdx.vertices.rawValue)
+    // Ideal as long as our uniforms total 4 KB or less
+    encoder.setVertexBytes(&uniforms,
+      length: MemoryLayout<ShaderUniforms>.stride,
+      index: ShaderInputIdx.uniforms.rawValue)
     encoder.drawIndexedPrimitives(
       type: .triangle,
       indexCount: cubeIndices.count,

Sources/Voxelotl/shader.metal

@@ -12,10 +12,14 @@ struct FragmentInput {
 
 vertex FragmentInput vertexMain(
   uint vertexID [[vertex_id]],
-  device const ShaderVertex* vtx [[buffer(ShaderInputIdxVertices)]]
+  device const ShaderVertex* vtx [[buffer(ShaderInputIdxVertices)]],
+  constant ShaderUniforms& u [[buffer(ShaderInputIdxUniforms)]]
 ) {
+  auto position = vtx[vertexID].position;
+  position = u.projView * u.model * position;
+
   FragmentInput out;
-  out.position = vtx[vertexID].position * float4(0.5, 0.5, 0.5, 1.0);
+  out.position = position;
   out.normal   = vtx[vertexID].normal;
   out.texCoord = vtx[vertexID].texCoord;
   return out;

Sources/Voxelotl/shadertypes.h

@@ -11,7 +11,8 @@
 #include <simd/simd.h>
 
 typedef NS_ENUM(NSInteger, ShaderInputIdx) {
-  ShaderInputIdxVertices = 0
+  ShaderInputIdxVertices = 0,
+  ShaderInputIdxUniforms = 1
 };
 
 typedef struct {
@@ -20,4 +21,9 @@ typedef struct {
   vector_float2 texCoord;
 } ShaderVertex;
 
+typedef struct {
+  matrix_float4x4 model;
+  matrix_float4x4 projView;
+} ShaderUniforms;
+
 #endif//SHADERTYPES_H