Simplify lessons that use textured shaders w/o tinting

src/shaders/lesson8.metal

@@ -0,0 +1,45 @@
+/*
+ * SPDX-FileCopyrightText: (C) 2025 a dinosaur
+ * SPDX-License-Identifier: Zlib
+ */
+
+#include <metal_stdlib>
+#include <simd/simd.h>
+
+struct VertexInput
+{
+	float3 position [[attribute(0)]];
+	float2 texcoord [[attribute(1)]];
+};
+
+struct VertexUniform
+{
+	metal::float4x4 viewproj;
+	float4 color;
+};
+
+struct Vertex2Fragment
+{
+	float4 position [[position]];
+	float2 texcoord;
+	half4 color;
+};
+
+vertex Vertex2Fragment VertexMain(
+	VertexInput in [[stage_in]],
+	constant VertexUniform& u [[buffer(0)]])
+{
+	Vertex2Fragment out;
+	out.position = u.viewproj * float4(in.position, 1.0);
+	out.texcoord = in.texcoord;
+	out.color = half4(u.color);
+	return out;
+}
+
+fragment half4 FragmentMain(
+	Vertex2Fragment in [[stage_in]],
+	metal::texture2d<half, metal::access::sample> texture [[texture(0)]],
+	metal::sampler sampler [[sampler(0)]])
+{
+	return in.color * texture.sample(sampler, in.texcoord);
+}