gl: Add tex.compare func support

src/rhi/qrhigles2.cpp

@@ -200,6 +200,18 @@ QT_BEGIN_NAMESPACE
 #define GL_MAX_DRAW_BUFFERS               0x8824
 #endif
 
+#ifndef GL_TEXTURE_COMPARE_MODE
+#define GL_TEXTURE_COMPARE_MODE           0x884C
+#endif
+
+#ifndef GL_COMPARE_REF_TO_TEXTURE
+#define GL_COMPARE_REF_TO_TEXTURE         0x884E
+#endif
+
+#ifndef GL_TEXTURE_COMPARE_FUNC
+#define GL_TEXTURE_COMPARE_FUNC           0x884D
+#endif
+
 static QSurfaceFormat qrhigles2_effectiveFormat()
 {
     QSurfaceFormat fmt = QSurfaceFormat::defaultFormat();
@@ -1330,6 +1342,31 @@ static inline GLenum toGlWrapMode(QRhiSampler::AddressMode m)
     }
 }
 
+static inline GLenum toGlTextureCompareFunc(QRhiSampler::CompareOp op)
+{
+    switch (op) {
+    case QRhiSampler::Never:
+        return GL_NEVER;
+    case QRhiSampler::Less:
+        return GL_LESS;
+    case QRhiSampler::Equal:
+        return GL_EQUAL;
+    case QRhiSampler::LessOrEqual:
+        return GL_LEQUAL;
+    case QRhiSampler::Greater:
+        return GL_GREATER;
+    case QRhiSampler::NotEqual:
+        return GL_NOTEQUAL;
+    case QRhiSampler::GreaterOrEqual:
+        return GL_GEQUAL;
+    case QRhiSampler::Always:
+        return GL_ALWAYS;
+    default:
+        Q_UNREACHABLE();
+        return GL_NEVER;
+    }
+}
+
 void QRhiGles2::executeCommandBuffer(QRhiCommandBuffer *cb)
 {
     QGles2CommandBuffer *cbD = QRHI_RES(QGles2CommandBuffer, cb);
@@ -1762,6 +1799,12 @@ void QRhiGles2::setChangedUniforms(QRhiGraphicsPipeline *ps, QRhiShaderResourceB
                         f->glTexParameteri(texD->target, GL_TEXTURE_WRAP_S, samplerD->glwraps);
                         f->glTexParameteri(texD->target, GL_TEXTURE_WRAP_T, samplerD->glwrapt);
                         f->glTexParameteri(texD->target, GL_TEXTURE_WRAP_R, samplerD->glwrapr);
+                        if (samplerD->gltexcomparefunc != GL_NEVER) {
+                            f->glTexParameteri(texD->target, GL_TEXTURE_COMPARE_MODE, GL_COMPARE_REF_TO_TEXTURE);
+                            f->glTexParameteri(texD->target, GL_TEXTURE_COMPARE_FUNC, samplerD->gltexcomparefunc);
+                        } else {
+                            f->glTexParameteri(texD->target, GL_TEXTURE_COMPARE_MODE, GL_NONE);
+                        }
                     }
 
                     f->glUniform1i(sampler.glslLocation, texUnit);
@@ -2242,6 +2285,7 @@ bool QGles2Sampler::build()
     glwraps = toGlWrapMode(m_addressU);
     glwrapt = toGlWrapMode(m_addressV);
     glwrapr = toGlWrapMode(m_addressW);
+    gltexcomparefunc = toGlTextureCompareFunc(m_compareOp);
 
     generation += 1;
     return true;

src/rhi/qrhigles2_p.h

@@ -113,6 +113,7 @@ struct QGles2Sampler : public QRhiSampler
     GLenum glwraps;
     GLenum glwrapt;
     GLenum glwrapr;
+    GLenum gltexcomparefunc;
 
     uint generation = 0;
     friend class QRhiGles2;