rhi: gl: Have a way to state GL_TEXTURE_RECTANGLE is wanted

Added specifically to support the deprecated CVOpenGLTextureCache on
macOS, because Qt Multimedia still needs a way to use that when the
applications requests using OpenGL instead of Metal.

Follow what we did for GL_TEXTURE_EXTERNAL_OES, and add a flag that
simply makes all our glBindTexture calls use the
GL_TEXTURE_RECTANGLE[_ARB] target.

Pick-to: 6.2
Change-Id: If818b13a9f520cdb8bdc16de84a3ca0e18ad6c33
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/rhi/qrhi.cpp

@@ -2444,6 +2444,13 @@ bool QRhiRenderBuffer::createFrom(NativeRenderBuffer src)
      render target's color attachment refers to a slice in range [0..depth-1].
      The underlying graphics API may not support 3D textures at run time.
      Support is indicated by the QRhi::ThreeDimensionalTextures feature.
+
+     \value TextureRectangleGL The texture should use the GL_TEXTURE_RECTANGLE
+     target with OpenGL. This flag is ignored with other graphics APIs. Just
+     like ExternalOES, this flag is useful when working with platform APIs where
+     native OpenGL texture objects received from the platform are wrapped in a
+     QRhiTexture, and the platform can only provide textures for a non-2D
+     texture target.
  */
 
 /*!

src/gui/rhi/qrhi_p.h

@@ -778,7 +778,8 @@ public:
         UsedWithLoadStore = 1 << 7,
         UsedAsCompressedAtlas = 1 << 8,
         ExternalOES = 1 << 9,
-        ThreeDimensional = 1 << 10
+        ThreeDimensional = 1 << 10,
+        TextureRectangleGL = 1 << 11
     };
     Q_DECLARE_FLAGS(Flags, Flag)
 

src/gui/rhi/qrhigles2.cpp

@@ -361,6 +361,10 @@ QT_BEGIN_NAMESPACE
 #define GL_TEXTURE_WRAP_R                 0x8072
 #endif
 
+#ifndef GL_TEXTURE_RECTANGLE
+#define GL_TEXTURE_RECTANGLE              0x84F5
+#endif
+
 /*!
     Constructs a new QRhiGles2InitParams.
 
@@ -4579,6 +4583,8 @@ bool QGles2Texture::prepareCreate(QSize *adjustedSize)
                     : m_sampleCount > 1 ? GL_TEXTURE_2D_MULTISAMPLE : (is3D ? GL_TEXTURE_3D : GL_TEXTURE_2D);
     if (m_flags.testFlag(ExternalOES))
         target = GL_TEXTURE_EXTERNAL_OES;
+    else if (m_flags.testFlag(TextureRectangleGL))
+        target = GL_TEXTURE_RECTANGLE;
 
     mipLevelCount = hasMipMaps ? rhiD->q->mipLevelsForSize(size) : 1;
     gltype = GL_UNSIGNED_BYTE;