rhi: gl: Add some enablers for supporting GL_TEXTURE_EXTERNAL_OES

From QRhi's perspective this consists of two things:

- A shader with samplerExternalOES in it cannot go through the standard
  pipeline. Rather, a QShader with suitable GLSL code in it has to be
  constructed manually. As this is something useful as an autotest
  anyway, add a test case to the qshader autotest that demonstrates
  this.

- When it comes to correctly calling glBindTexture, add a QRhiTexture
  flag. The expectation is that an OpenGL-only client sets this in
  combination with QRhiTexture::createFrom(), thus wrapping an existing
  texture that then gets bound to the GL_TEXTURE_EXTERNAL_OES target
  instead of our usual GL_TEXTURE_2D.

For completeness we also add a SamplerExternalOES variable type to
QShaderDescription, but the sampler type is not actually used by the
QRhi OpenGL backend, as it is the QRhiTexture that defines the
texture target.

Change-Id: I36b52325deb3703b59186ee3d726d0c3015bfc4b
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index fc65587408..647f469dcf 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -745,7 +745,8 @@ public:
         UsedAsTransferSource = 1 << 5,
         UsedWithGenerateMips = 1 << 6,
         UsedWithLoadStore = 1 << 7,
-        UsedAsCompressedAtlas = 1 << 8
+        UsedAsCompressedAtlas = 1 << 8,
+        ExternalOES = 1 << 9
     };
     Q_DECLARE_FLAGS(Flags, Flag)