Add test of degenerate vertex shaders with no outputs but full GS output

util/test/demos/gl/gl_mesh_zoo.cpp

@@ -75,6 +75,40 @@ void main()
 	Color = col;
 }
 
+)EOSHADER";
+
+  std::string nopvertex = R"EOSHADER(
+#version 420 core
+
+void main()
+{
+}
+
+)EOSHADER";
+
+  std::string geometry = R"EOSHADER(
+#version 420 core
+
+layout(points) in;
+layout(triangle_strip, max_vertices = 3) out;
+
+out vec4 col;
+
+void main()
+{
+  const vec4 verts[3] = vec4[3](vec4(-0.4, -0.4, 0.5, 1.0), vec4(0.6, -0.6, 0.5, 1.0),
+                                vec4(-0.5, 0.5, 0.5, 1.0));
+
+  for(int i=0; i < 3; i++)
+  {
+    gl_Position = verts[i];
+    col = vec4(1, 0, 0, 1);
+    EmitVertex();
+  }
+
+  EndPrimitive();
+}
+
 )EOSHADER";
 
   int main()
@@ -152,6 +186,8 @@ void main()
 
     GLuint program = MakeProgram(common + vertex, common + pixel);
 
+    GLuint geomprogram = MakeProgram(nopvertex, common + pixel, geometry);
+
     GLuint fbo = MakeFBO();
     glBindFramebuffer(GL_FRAMEBUFFER, fbo);
 
@@ -201,6 +237,12 @@ void main()
 
       glDrawArrays(GL_POINTS, 0, 1);
 
+      setMarker("Geom Only");
+
+      glUseProgram(geomprogram);
+
+      glDrawArrays(GL_POINTS, 0, 1);
+
       glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
       glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
       glBlitFramebuffer(0, 0, screenWidth, screenHeight, 0, 0, screenWidth, screenHeight,

util/test/tests/GL/GL_Mesh_Zoo.py

@@ -10,4 +10,33 @@ class GL_Mesh_Zoo(rdtest.TestCase):
         self.zoo_helper = rdtest.Mesh_Zoo()
 
     def check_capture(self):
-        self.zoo_helper.check_capture(self.capture_filename, self.controller)
+        self.zoo_helper.check_capture(self.capture_filename, self.controller)
+
+        # Test GL-only thing with geometry shader only and completely no-op vertex shader
+        self.controller.SetFrameEvent(self.zoo_helper.find_draw("Geom Only").next.eventId, False)
+
+        pos: rd.MeshFormat = self.controller.GetPostVSData(0, 0, rd.MeshDataStage.VSOut)
+
+        # vertex output should be completely empty
+        self.check(pos.vertexByteStride == 0)
+        self.check(pos.numIndices == 0)
+        self.check(self.controller.GetBufferData(pos.vertexResourceId, 0, 0) == bytes())
+
+        gsout_ref = {
+            0: {
+                'gl_Position': [-0.4, -0.4, 0.5, 1.0],
+                'col': [1.0, 0.0, 0.0, 1.0],
+            },
+            1: {
+                'gl_Position': [0.6, -0.6, 0.5, 1.0],
+                'col': [1.0, 0.0, 0.0, 1.0],
+            },
+            2: {
+                'gl_Position': [-0.5, 0.5, 0.5, 1.0],
+                'col': [1.0, 0.0, 0.0, 1.0],
+            },
+        }
+
+        self.check_mesh_data(gsout_ref, self.get_postvs(rd.MeshDataStage.GSOut))
+
+        rdtest.log.success("Geometry-only pass is as expected")