Add RHI feature check for screen space derivatives

Fragment shader functions like fwidth() are useful for antialiasing
distance field text in the case of perspective projections. In order
to enable this as an alternative code path, we need to detect support.

- OpenGL: Supported with GL_OES_standard_derivatives or GLES3 and up
- Direct 3D: Supported for ps_2_x, so always supported on Direct3D 11
- Vulkan/Metal: Always supported

Task-number: QTBUG-84695
Change-Id: I5e3fa8014c808a9a2d639305c5e90ec25d44655c
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

8 files changed, 22 insertions, 3 deletions

diff --git a/src/gui/opengl/qopenglextensions_p.h b/src/gui/opengl/qopenglextensions_p.h
index 137f1e831f..0d58b5f301 100644
--- a/src/gui/opengl/qopenglextensions_p.h
+++ b/src/gui/opengl/qopenglextensions_p.h
@@ -92,6 +92,7 @@ public:
         DiscardFramebuffer      = 0x00400000,
         Sized16Formats          = 0x00800000,
         TextureSwizzle          = 0x01000000,
+        StandardDerivatives     = 0x02000000,
     };
     Q_DECLARE_FLAGS(OpenGLExtensions, OpenGLExtension)
 
diff --git a/src/gui/opengl/qopenglfunctions.cpp b/src/gui/opengl/qopenglfunctions.cpp
index a95f064ac5..7c17d3798b 100644
--- a/src/gui/opengl/qopenglfunctions.cpp
+++ b/src/gui/opengl/qopenglfunctions.cpp
@@ -376,6 +376,8 @@ static int qt_gl_resolve_extensions()
         extensions |= QOpenGLExtensions::PixelBufferObject;
     if (extensionMatcher.match("GL_ARB_texture_swizzle") || extensionMatcher.match("GL_EXT_texture_swizzle"))
         extensions |= QOpenGLExtensions::TextureSwizzle;
+    if (extensionMatcher.match("GL_OES_standard_derivatives"))
+        extensions |= QOpenGLExtensions::StandardDerivatives;
 
     if (ctx->isOpenGLES()) {
         if (format.majorVersion() >= 2)
@@ -388,7 +390,8 @@ static int qt_gl_resolve_extensions()
                 | QOpenGLExtensions::MapBufferRange
                 | QOpenGLExtensions::FramebufferBlit
                 | QOpenGLExtensions::FramebufferMultisample
-                | QOpenGLExtensions::Sized8Formats;
+                | QOpenGLExtensions::Sized8Formats
+                | QOpenGLExtensions::StandardDerivatives;
 #ifndef Q_OS_WASM
             // WebGL 2.0 specification explicitly does not support texture swizzles
             // https://www.khronos.org/registry/webgl/specs/latest/2.0/#5.19
@@ -445,6 +448,9 @@ static int qt_gl_resolve_extensions()
         if (format.version() >= qMakePair(1, 4) || extensionMatcher.match("GL_SGIS_generate_mipmap"))
             extensions |= QOpenGLExtensions::GenerateMipmap;
 
+        if (format.majorVersion() >= 2)
+            extensions |= QOpenGLExtensions::StandardDerivatives;
+
         if (format.majorVersion() >= 3 || extensionMatcher.match("GL_ARB_framebuffer_object")) {
             extensions |= QOpenGLExtensions::FramebufferMultisample
                 | QOpenGLExtensions::FramebufferBlit
diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index bd476c3927..9f94fea1dc 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -1456,7 +1456,8 @@ public:
         ReadBackNonBaseMipLevel,
         TexelFetch,
         RenderToNonBaseMipLevel,
-        UIntAttributes
+        UIntAttributes,
+        ScreenSpaceDerivatives
     };
 
     enum BeginFrameFlag {
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index c284e17f46..710ebd62cc 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -479,6 +479,8 @@ bool QRhiD3D11::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::UIntAttributes:
         return true;
+    case QRhi::ScreenSpaceDerivatives:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;
diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index ebe66f302b..632a5154e7 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -522,6 +522,7 @@ bool QRhiGles2::create(QRhi::Flags flags)
 
     caps.texelFetch = caps.ctxMajor >= 3; // 3.0 or ES 3.0
     caps.uintAttributes = caps.ctxMajor >= 3; // 3.0 or ES 3.0
+    caps.screenSpaceDerivatives = f->hasOpenGLExtension(QOpenGLExtensions::StandardDerivatives);
 
     if (!caps.gles) {
         f->glEnable(GL_VERTEX_PROGRAM_POINT_SIZE);
@@ -872,6 +873,8 @@ bool QRhiGles2::isFeatureSupported(QRhi::Feature feature) const
         return caps.nonBaseLevelFramebufferTexture;
     case QRhi::UIntAttributes:
         return caps.uintAttributes;
+    case QRhi::ScreenSpaceDerivatives:
+        return caps.screenSpaceDerivatives;
     default:
         Q_UNREACHABLE();
         return false;
diff --git a/src/gui/rhi/qrhigles2_p_p.h b/src/gui/rhi/qrhigles2_p_p.h
index 2c393da3b4..03ed81dfb2 100644
--- a/src/gui/rhi/qrhigles2_p_p.h
+++ b/src/gui/rhi/qrhigles2_p_p.h
@@ -869,7 +869,8 @@ public:
               properMapBuffer(false),
               nonBaseLevelFramebufferTexture(false),
               texelFetch(false),
-              uintAttributes(true)
+              uintAttributes(true),
+              screenSpaceDerivatives(false)
         { }
         int ctxMajor;
         int ctxMinor;
@@ -904,6 +905,7 @@ public:
         uint nonBaseLevelFramebufferTexture : 1;
         uint texelFetch : 1;
         uint uintAttributes : 1;
+        uint screenSpaceDerivatives : 1;
     } caps;
     QGles2SwapChain *currentSwapChain = nullptr;
     QVector<GLint> supportedCompressedFormats;
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index b249dc55cc..0c42eaa3e9 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -568,6 +568,8 @@ bool QRhiMetal::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::UIntAttributes:
         return true;
+    case QRhi::ScreenSpaceDerivatives:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index 59898d3839..fdc80e1e80 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -4050,6 +4050,8 @@ bool QRhiVulkan::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::UIntAttributes:
         return true;
+    case QRhi::ScreenSpaceDerivatives:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;