rhi: Expose the maximum uniform buffer range limit

Pick-to: 6.2
Task-number: QTBUG-97715
Change-Id: I7f0a52c410b9b77f735fb3b7fd33141674bb0cda
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

8 files changed, 62 insertions, 1 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index efa3c1893d..952183f55e 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -776,6 +776,12 @@ Q_LOGGING_CATEGORY(QRHI_LOG_INFO, "qt.rhi.general")
     \value TextureArraySizeMax Maximum texture array size. Typically in range
     256 - 2048. Attempting to \l{QRhi::newTextureArray()}{create a texture
     array} with more elements will likely fail.
+
+    \value MaxUniformBufferRange The number of bytes that can be exposed from a
+    uniform buffer to the shaders at once. On OpenGL ES 2.0 and 3.0
+    implementations this may be as low as 3584 bytes (224 four component, 32
+    bits per component vectors). Elsewhere the value is typically 16384 (1024
+    vec4s) or 65536 (4096 vec4s).
  */
 
 /*!
@@ -3228,6 +3234,9 @@ bool QRhiShaderResourceBinding::isLayoutCompatible(const QRhiShaderResourceBindi
     suitable for creating pipelines. Such a pipeline must then always be used
     together with another, layout compatible QRhiShaderResourceBindings with
     resources present passed to QRhiCommandBuffer::setShaderResources().
+
+    \note If the size of \a buf exceeds the limit reported for
+    QRhi::MaxUniformBufferRange, unexpected errors may occur.
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
         int binding, StageFlags stage, QRhiBuffer *buf)
@@ -3262,6 +3271,9 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
     suitable for creating pipelines. Such a pipeline must then always be used
     together with another, layout compatible QRhiShaderResourceBindings with
     resources present passed to QRhiCommandBuffer::setShaderResources().
+
+    \note If \a size exceeds the limit reported for QRhi::MaxUniformBufferRange,
+    unexpected errors may occur.
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
         int binding, StageFlags stage, QRhiBuffer *buf, int offset, int size)
@@ -3296,6 +3308,9 @@ QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBuffer(
     suitable for creating pipelines. Such a pipeline must then always be used
     together with another, layout compatible QRhiShaderResourceBindings with
     resources present passed to QRhiCommandBuffer::setShaderResources().
+
+    \note If \a size exceeds the limit reported for QRhi::MaxUniformBufferRange,
+    unexpected errors may occur.
  */
 QRhiShaderResourceBinding QRhiShaderResourceBinding::uniformBufferWithDynamicOffset(
         int binding, StageFlags stage, QRhiBuffer *buf, int size)
diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index 4decdd0c91..5344046841 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -1612,7 +1612,8 @@ public:
         MaxThreadGroupX,
         MaxThreadGroupY,
         MaxThreadGroupZ,
-        TextureArraySizeMax
+        TextureArraySizeMax,
+        MaxUniformBufferRange
     };
 
     ~QRhi();
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index 631e7f7adf..d2b217b6d4 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -580,6 +580,8 @@ int QRhiD3D11::resourceLimit(QRhi::ResourceLimit limit) const
         return D3D11_CS_THREAD_GROUP_MAX_Z;
     case QRhi::TextureArraySizeMax:
         return D3D11_REQ_TEXTURE2D_ARRAY_AXIS_DIMENSION;
+    case QRhi::MaxUniformBufferRange:
+        return 65536;
     default:
         Q_UNREACHABLE();
         return 0;
diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index 5259be270c..4512acb969 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -405,6 +405,22 @@ QT_BEGIN_NAMESPACE
 #define GL_MAX_ARRAY_TEXTURE_LAYERS       0x88FF
 #endif
 
+#ifndef GL_MAX_VERTEX_UNIFORM_COMPONENTS
+#define GL_MAX_VERTEX_UNIFORM_COMPONENTS  0x8B4A
+#endif
+
+#ifndef GL_MAX_FRAGMENT_UNIFORM_COMPONENTS
+#define GL_MAX_FRAGMENT_UNIFORM_COMPONENTS 0x8B49
+#endif
+
+#ifndef GL_MAX_VERTEX_UNIFORM_VECTORS
+#define GL_MAX_VERTEX_UNIFORM_VECTORS     0x8DFB
+#endif
+
+#ifndef GL_MAX_FRAGMENT_UNIFORM_VECTORS
+#define GL_MAX_FRAGMENT_UNIFORM_VECTORS   0x8DFD
+#endif
+
 /*!
     Constructs a new QRhiGles2InitParams.
 
@@ -694,6 +710,23 @@ bool QRhiGles2::create(QRhi::Flags flags)
         caps.maxTextureArraySize = 0;
     }
 
+    // The ES 2.0 spec only has MAX_xxxx_VECTORS. ES 3.0 and up has both
+    // *VECTORS and *COMPONENTS. OpenGL 2.0-4.0 only has MAX_xxxx_COMPONENTS.
+    // 4.1 and above has both. What a mess.
+    if (caps.gles) {
+        GLint maxVertexUniformVectors = 0;
+        f->glGetIntegerv(GL_MAX_VERTEX_UNIFORM_VECTORS, &maxVertexUniformVectors);
+        GLint maxFragmentUniformVectors = 0;
+        f->glGetIntegerv(GL_MAX_FRAGMENT_UNIFORM_VECTORS, &maxFragmentUniformVectors);
+        caps.maxUniformVectors = qMin(maxVertexUniformVectors, maxFragmentUniformVectors);
+    } else {
+        GLint maxVertexUniformComponents = 0;
+        f->glGetIntegerv(GL_MAX_VERTEX_UNIFORM_COMPONENTS, &maxVertexUniformComponents);
+        GLint maxFragmentUniformComponents = 0;
+        f->glGetIntegerv(GL_MAX_FRAGMENT_UNIFORM_COMPONENTS, &maxFragmentUniformComponents);
+        caps.maxUniformVectors = qMin(maxVertexUniformComponents, maxFragmentUniformComponents) / 4;
+    }
+
     if (!caps.gles) {
         f->glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
         f->glEnable(GL_POINT_SPRITE);
@@ -1125,6 +1158,8 @@ int QRhiGles2::resourceLimit(QRhi::ResourceLimit limit) const
         return caps.maxThreadGroupsZ;
     case QRhi::TextureArraySizeMax:
         return 2048;
+    case QRhi::MaxUniformBufferRange:
+        return int(qMin<qint64>(INT_MAX, caps.maxUniformVectors * qint64(16)));
     default:
         Q_UNREACHABLE();
         return 0;
diff --git a/src/gui/rhi/qrhigles2_p_p.h b/src/gui/rhi/qrhigles2_p_p.h
index 48f79e3c1d..c3297f488d 100644
--- a/src/gui/rhi/qrhigles2_p_p.h
+++ b/src/gui/rhi/qrhigles2_p_p.h
@@ -918,6 +918,7 @@ public:
               maxThreadGroupsX(0),
               maxThreadGroupsY(0),
               maxThreadGroupsZ(0),
+              maxUniformVectors(4096),
               msaaRenderBuffer(false),
               multisampledTexture(false),
               npotTextureFull(true),
@@ -960,6 +961,7 @@ public:
         int maxThreadGroupsX;
         int maxThreadGroupsY;
         int maxThreadGroupsZ;
+        int maxUniformVectors;
         // Multisample fb and blit are supported (GLES 3.0 or OpenGL 3.x). Not
         // the same as multisample textures!
         uint msaaRenderBuffer : 1;
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index 3e4c0e08e2..169d80251d 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -650,6 +650,8 @@ int QRhiMetal::resourceLimit(QRhi::ResourceLimit limit) const
 #endif
     case QRhi::TextureArraySizeMax:
         return 2048;
+    case QRhi::MaxUniformBufferRange:
+        return 65536;
     default:
         Q_UNREACHABLE();
         return 0;
diff --git a/src/gui/rhi/qrhinull.cpp b/src/gui/rhi/qrhinull.cpp
index c160958493..b23af75bd9 100644
--- a/src/gui/rhi/qrhinull.cpp
+++ b/src/gui/rhi/qrhinull.cpp
@@ -164,6 +164,8 @@ int QRhiNull::resourceLimit(QRhi::ResourceLimit limit) const
         return 0;
     case QRhi::TextureArraySizeMax:
         return 2048;
+    case QRhi::MaxUniformBufferRange:
+        return 65536;
     default:
         Q_UNREACHABLE();
         return 0;
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index c0d5ab1c07..1cead19f77 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -4305,6 +4305,8 @@ int QRhiVulkan::resourceLimit(QRhi::ResourceLimit limit) const
         return int(physDevProperties.limits.maxComputeWorkGroupSize[2]);
     case QRhi::TextureArraySizeMax:
         return int(physDevProperties.limits.maxImageArrayLayers);
+    case QRhi::MaxUniformBufferRange:
+        return int(qMin<uint32_t>(INT_MAX, physDevProperties.limits.maxUniformBufferRange));
     default:
         Q_UNREACHABLE();
         return 0;