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 <[email protected]>

8 files changed, 22 insertions, 3 deletions

diff --git a/src/gui/opengl/qopenglextensions_p.h b/src/gui/opengl/qopenglextensions_p.h
index 137f1e831f7..0d58b5f301d 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 a95f064ac56..7c17d3798bd 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 bd476c39273..9f94fea1dc0 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 c284e17f469..710ebd62cc3 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 ebe66f302bb..632a5154e7b 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 2c393da3b4e..03ed81dfb28 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 b249dc55ccb..0c42eaa3e9d 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 59898d3839e..fdc80e1e80f 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;