add sbuftex-sapp.glsl test shader

test/sapp/sbuftex-sapp.glsl

@@ -0,0 +1,50 @@
+@ctype mat4 hmm_mat4
+
+@vs vs
+layout(binding=0) uniform vs_params {
+    mat4 mvp;
+};
+
+struct sb_vertex {
+    vec3 pos;
+    uint idx;
+    vec2 uv;
+};
+
+layout(binding=0) readonly buffer vertices {
+    sb_vertex vtx[];
+};
+
+out vec3 uv_idx;
+
+void main() {
+    gl_Position = mvp * vec4(vtx[gl_VertexIndex].pos, 1.0);
+    // need to add a bit of wiggle room here to prevent a precision problem on NVIDIA
+    // down in the pixel shader
+    uv_idx = vec3(vtx[gl_VertexIndex].uv, float(vtx[gl_VertexIndex].idx) + 0.5);
+}
+@end
+
+@fs fs
+layout(binding=0) uniform texture2D tex;
+layout(binding=0) uniform sampler smp;
+
+struct sb_color {
+    vec4 color;
+};
+
+layout(binding=1) readonly buffer colors {
+    sb_color clr[];
+};
+
+in vec3 uv_idx;
+out vec4 frag_color;
+
+void main() {
+    uint idx = uint(uv_idx.z);
+    vec2 uv = uv_idx.xy;
+    frag_color = vec4(texture(sampler2D(tex,smp), uv).xxx, 1.0) * clr[idx].color;
+}
+@end
+
+@program sbuftex vs fs