Added draw package as renderer focused on mixed use layout / 2D / 3D scene applications (#7)

Co-authored-by: Zachary Levy <zachary@sunforge.is>
Reviewed-on: #7

draw/shaders/source/base_2d.vert

@@ -0,0 +1,67 @@
+#version 450 core
+
+// ---------- Vertex attributes (used in both modes) ----------
+layout(location = 0) in vec2 v_position;
+layout(location = 1) in vec2 v_uv;
+layout(location = 2) in vec4 v_color;
+
+// ---------- Outputs to fragment shader ----------
+layout(location = 0) out vec4 f_color;
+layout(location = 1) out vec2 f_local_or_uv;
+layout(location = 2) out vec4 f_params;
+layout(location = 3) out vec4 f_params2;
+layout(location = 4) flat out uint f_kind_flags;
+layout(location = 5) flat out float f_rotation;
+
+// ---------- Uniforms (single block — avoids spirv-cross reordering on Metal) ----------
+layout(set = 1, binding = 0) uniform Uniforms {
+    mat4 projection;
+    float dpi_scale;
+    uint mode; // 0 = tessellated, 1 = SDF
+};
+
+// ---------- SDF primitive storage buffer ----------
+struct Primitive {
+    vec4 bounds; // 0-15:  min_x, min_y, max_x, max_y
+    uint color; // 16-19: packed u8x4 (unpack with unpackUnorm4x8)
+    uint kind_flags; // 20-23: kind | (flags << 8)
+    float rotation; // 24-27: shader self-rotation in radians
+    float _pad; // 28-31: alignment padding
+    vec4 params; // 32-47: shape params part 1
+    vec4 params2; // 48-63: shape params part 2
+};
+
+layout(std430, set = 0, binding = 0) readonly buffer Primitives {
+    Primitive primitives[];
+};
+
+// ---------- Entry point ----------
+void main() {
+    if (mode == 0u) {
+        // ---- Mode 0: Tessellated (legacy) ----
+        f_color = v_color;
+        f_local_or_uv = v_uv;
+        f_params = vec4(0.0);
+        f_params2 = vec4(0.0);
+        f_kind_flags = 0u;
+        f_rotation = 0.0;
+
+        gl_Position = projection * vec4(v_position * dpi_scale, 0.0, 1.0);
+    } else {
+        // ---- Mode 1: SDF instanced quads ----
+        Primitive p = primitives[gl_InstanceIndex];
+
+        vec2 corner = v_position; // unit quad corners: (0,0)-(1,1)
+        vec2 world_pos = mix(p.bounds.xy, p.bounds.zw, corner);
+        vec2 center = 0.5 * (p.bounds.xy + p.bounds.zw);
+
+        f_color = unpackUnorm4x8(p.color);
+        f_local_or_uv = (world_pos - center) * dpi_scale; // shape-centered physical pixels
+        f_params = p.params;
+        f_params2 = p.params2;
+        f_kind_flags = p.kind_flags;
+        f_rotation = p.rotation;
+
+        gl_Position = projection * vec4(world_pos * dpi_scale, 0.0, 1.0);
+    }
+}