Add another triangle for occlusion

occlusion.cc

   vkCmdBeginRenderPass(command_buffer, &render_pass_begin_info, VK_SUBPASS_CONTENTS_INLINE);
 
   vkCmdBindPipeline(command_buffer, VK_PIPELINE_BIND_POINT_GRAPHICS, pipeline);
-  vkCmdDraw(command_buffer, 3, 1, 0, 0);
+  vkCmdDraw(command_buffer, 6, 1, 0, 0);
   vkCmdEndRenderPass(command_buffer);
   EndQuery(command_buffer, query_pool);
 }

occlusion.frag

 #version 450
 
+layout(location = 0) in vec3 fragColor;
+
 layout(location = 0) out vec4 outColor;
 
 void main() {
-    outColor = vec4(1.0, 0.0, 0.0, 1.0);
+    outColor = vec4(fragColor, 1.0);
 }

occlusion.vert

 #version 450
 
-vec2 positions[3] = vec2[](
-    vec2(0.0, -0.5),
-    vec2(0.5, 0.5),
-    vec2(-0.5, 0.5)
+layout(location = 0) out vec3 fragColor;
+
+vec3 positions[6] = vec3[](
+    vec3(0.5, -0.5, 1.0),
+    vec3(0.5, 0.5, 1.0),
+    vec3(-0.5, 0.5, 1.0),
+    vec3(-0.5, -0.5, 0.0),
+    vec3(0.5, 0.5, 0.0),
+    vec3(-0.5, 0.5, 0.0)
+);
+
+vec3 colors[6] = vec3[](
+    vec3(1.0, 0.0, 0.0),
+    vec3(1.0, 0.0, 0.0),
+    vec3(1.0, 0.0, 0.0),
+    vec3(0.0, 1.0, 0.0),
+    vec3(0.0, 1.0, 0.0),
+    vec3(0.0, 1.0, 0.0)
 );
 
 void main() {
-    gl_Position = vec4(positions[gl_VertexIndex], 0.0, 1.0);
+    gl_Position = vec4(positions[gl_VertexIndex], 1.0);
+    fragColor = colors[gl_VertexIndex];
 }