Extend shader compiler define syntax to allow name=value instead of just valueless defines

data/shaders/clip.vert

@@ -1,5 +1,6 @@
 #version 450
 #extension GL_ARB_separate_shader_objects : enable
+#pragma import_defines (NUM_CLIPS)
 
 layout(push_constant) uniform PushConstants {
     mat4 projection;
@@ -19,7 +20,9 @@ layout(location = 1) out vec2 fragTexCoord;
 
 out gl_PerVertex {
     vec4 gl_Position;
-    float gl_ClipDistance[1];
+    #if NUM_CLIPS > 0
+        float gl_ClipDistance[NUM_CLIPS];
+    #endif
     //float gl_CullDistance[1];
 };
 
@@ -36,6 +39,16 @@ void main() {
 
     vec4 eye_Position = pc.modelview * vec4(inPosition, 1.0);
 
-    gl_ClipDistance[0] = (length(eye_Position.xyz - clipSettings.sphere.xyz) - clipSettings.sphere.w);
+    #if NUM_CLIPS > 0
+        for (uint cOffset = 0; cOffset < NUM_CLIPS; ++cOffset) {
+            if (cOffset == 0) {
+                // clip volume inside the sphere using eye coordinates
+                gl_ClipDistance[cOffset] = (length(eye_Position.xyz - clipSettings.sphere.xyz) - clipSettings.sphere.w);
+            } else if (cOffset == 1) {
+                // simple clip on world coordinate X less than zero
+               gl_ClipDistance[cOffset] = inPosition.x;
+            }
+        }
+    #endif
     // gl_CullDistance[0] = (length(inPosition - clipSettings.sphere.xyz) - 3.0);
 }

examples/state/vsgclip/vsgclip.cpp

@@ -130,6 +130,13 @@ int main(int argc, char** argv)
 
         auto numFrames = arguments.value(-1, "-f");
 
+        auto numClips = arguments.value(1, "-n");
+        if (numClips < 0 || numClips > 2)
+        {
+            std::cout << "Choose between 0 and 2 clips. If n is zero clipping is disabled. If n is 1 a clipping sphere is enabled in eye space, and if n is 2, world coordinate values less than X=0 are clipped in addition to the clipping sphere." << std::endl;
+            return 1;
+        }
+
         if (arguments.errors()) return arguments.writeErrorMessages(std::cerr);
 
         if (argc <= 1)
@@ -160,6 +167,10 @@ int main(int argc, char** argv)
             return 1;
         }
 
+        // specify the number of clips to perform; gl_ClipDistance array is sized by NUM_CLIPS
+        vertexShader->module->hints = vsg::ShaderCompileSettings::create();
+        vertexShader->module->hints->defines.insert("NUM_CLIPS="+std::to_string(numClips));
+
         // create the viewer and assign window(s) to it
         auto viewer = vsg::Viewer::create();