feat: implement canvas

Memola/Canvas/Shaders/Graphic.metal

@@ -0,0 +1,46 @@
+//
+//  Graphic.metal
+//  Memola
+//
+//  Created by Dscyre Scotti on 5/4/24.
+//
+
+#include <metal_stdlib>
+using namespace metal;
+
+struct VertexIn {
+    float4 position [[position]];
+    float2 textCoord;
+};
+
+struct VertexOut {
+    float4 position [[position]];
+    float2 textCoord;
+    float4 color;
+};
+
+struct Uniforms {
+    float4 color;
+};
+
+vertex VertexOut vertex_graphic(
+    constant VertexIn *vertices [[buffer(0)]],
+    constant Uniforms &uniforms [[buffer(11)]],
+    uint vertexId [[vertex_id]]
+) {
+    VertexIn in = vertices[vertexId];
+    VertexOut out;
+    out.position = in.position;
+    out.textCoord = in.textCoord;
+    out.color = uniforms.color;
+    return out;
+}
+
+fragment float4 fragment_graphic(
+    VertexOut out [[stage_in]],
+    texture2d<float> offscreenTexture [[texture(0)]]
+) {
+    constexpr sampler textureSampler(mag_filter::linear, min_filter::linear);
+    float4 color = float4(offscreenTexture.sample(textureSampler, out.textCoord));
+    return float4(out.color.rgb, color.a * out.color.a);
+}