initial sprite batch implementation & testbed

Sources/Voxelotl/shader2D.metal

@@ -0,0 +1,28 @@
+#include "shadertypes.h"
+#include <metal_stdlib>
+
+
+struct FragmentInput {
+  float4 position [[position]];
+  float2 texCoord;
+  half4  color;
+};
+
+vertex FragmentInput vertex2DMain(uint vertexID [[vertex_id]],
+  device const Vertex2D* vtx [[buffer(VertexShaderInputIdxVertices)]],
+  constant Shader2DUniforms& u [[buffer(VertexShaderInputIdxUniforms)]]
+) {
+  FragmentInput out;
+  out.position = u.projection * float4(vtx[vertexID].position, 0.0, 1.0);
+  out.texCoord = vtx[vertexID].texCoord;
+  out.color    = half4(vtx[vertexID].color);
+  return out;
+}
+
+fragment half4 fragment2DMain(FragmentInput in [[stage_in]],
+  metal::texture2d<half, metal::access::sample> texture [[texture(0)]]
+) {
+  constexpr metal::sampler sampler(metal::address::repeat, metal::filter::linear);
+  half4 texel = texture.sample(sampler, in.texCoord);
+  return texel * in.color;
+}