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>

5 files changed, 15 insertions, 1 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index 718835ad8f..838385aeed 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -2311,6 +2311,9 @@ QRhiResource::Type QRhiRenderBuffer::resourceType() const
 
      \value UsedAsCompressedAtlas The texture has a compressed format and the
      dimensions of subresource uploads may not match the texture size.
+
+     \value ExternalOES The texture should use the GL_TEXTURE_EXTERNAL_OES
+     target with OpenGL. This flag is ignored with other graphics APIs.
  */
 
 /*!
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)
 
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;
 
diff --git a/src/gui/rhi/qshaderdescription.cpp b/src/gui/rhi/qshaderdescription.cpp
index b20ed8b178..08972587ed 100644
--- a/src/gui/rhi/qshaderdescription.cpp
+++ b/src/gui/rhi/qshaderdescription.cpp
@@ -218,6 +218,7 @@ QT_BEGIN_NAMESPACE
     \value SamplerCubeArray
     \value SamplerRect
     \value SamplerBuffer
+    \value SamplerExternalOES
     \value Image1D
     \value Image2D
     \value Image2DMS
@@ -574,6 +575,7 @@ static struct TypeTab {
     { QLatin1String("samplerCubeArray"), QShaderDescription::SamplerCubeArray },
     { QLatin1String("samplerRect"), QShaderDescription::SamplerRect },
     { QLatin1String("samplerBuffer"), QShaderDescription::SamplerBuffer },
+    { QLatin1String("samplerExternalOES"), QShaderDescription::SamplerExternalOES },
 
     { QLatin1String("mat2x3"), QShaderDescription::Mat2x3 },
     { QLatin1String("mat2x4"), QShaderDescription::Mat2x4 },
diff --git a/src/gui/rhi/qshaderdescription_p.h b/src/gui/rhi/qshaderdescription_p.h
index 238efc2455..6879c531d3 100644
--- a/src/gui/rhi/qshaderdescription_p.h
+++ b/src/gui/rhi/qshaderdescription_p.h
@@ -133,6 +133,7 @@ public:
         SamplerCubeArray,
         SamplerRect,
         SamplerBuffer,
+        SamplerExternalOES,
 
         Image1D,
         Image2D,