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, 7 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index 014d603724..3c71086de0 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -305,6 +305,10 @@ QT_BEGIN_NAMESPACE
 #define GL_TEXTURE_2D_MULTISAMPLE         0x9100
 #endif
 
+#ifndef GL_TEXTURE_EXTERNAL_OES
+#define GL_TEXTURE_EXTERNAL_OES           0x8D65
+#endif
+
 #ifndef GL_MAX_COMPUTE_WORK_GROUP_INVOCATIONS
 #define GL_MAX_COMPUTE_WORK_GROUP_INVOCATIONS 0x90EB
 #endif
@@ -4134,6 +4138,9 @@ bool QGles2Texture::prepareCreate(QSize *adjustedSize)
 
     target = isCube ? GL_TEXTURE_CUBE_MAP
                     : m_sampleCount > 1 ? GL_TEXTURE_2D_MULTISAMPLE : GL_TEXTURE_2D;
+    if (m_flags.testFlag(ExternalOES))
+        target = GL_TEXTURE_EXTERNAL_OES;
+
     mipLevelCount = hasMipMaps ? rhiD->q->mipLevelsForSize(size) : 1;
     gltype = GL_UNSIGNED_BYTE;