Add QQuickPathItem and its backend infra

The generic backend uses the triangulator from QtGui, but is in
fact OpenGL-only for now due to materials.

The NVPR backend uses GL_NV_path_rendering on NVIDIA hardware with
OpenGL 4.3+ or OpenGL ES 3.1+.

The software backend simply uses QPainter.

With the generic backend each PathItem is backed by a non-visual root node
and 0, 1 or 2 child geometry nodes, depending on the presence of visible
stroking and filling. The potentially expensive triangulation happens on
updatePolish(), on the gui thread. This is proven to provide much smoother
results when compared to doing the geometry generation on the render thread
in updatePaintNode(), in particular on power-limited embedded devices.

The NVPR backend uses a QSGRenderNode in DepthAware mode so that the batch
renderer can continue to rely on the depth buffer and use opaque batches.
Due to not relying on slow CPU-side triangulation, this backend uses 5-10
times less CPU, even when properties of the path or its elements are
animated.

The path itself is specified with the PathView's Path, PathLine, PathArc,
PathQuad, etc. types. This allows for consistency with PathView and the
2D Canvas and avoids a naming mess in the API. However, there won't be a
100% symmetry: backends like NVPR will not rely on QPainterPath but process
the path elements on their own (as QPainterPath is essentially useless with
these APIs), which can lead to differences in the supported path elements.

The supported common set is currently Move, Line, Quad, Cubic, Arc.

The patch introduces PathMove, which is essentially PathLine but maps to
moveTo instead of lineTo. More types may get added later (e.g. NVPR can do
a wide variety of optimized rounded rects, but this requires directly
specifying a GL_ROUNDED_RECTx_NV command, thus neededing a dedicated Path
type on our side too)

For filling with gradients only linear gradients are supported at the
moment.

In addition to the declarative API, a more lightweight, QObject-less
JS-callable API should be considered as well for the future.

Change-Id: I335ad64b425ee279505d60e3e57ac6841e1cbd24
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 20 insertions, 4 deletions

diff --git a/src/quick/scenegraph/util/qsgtexture.cpp b/src/quick/scenegraph/util/qsgtexture.cpp
index 47248f2f37..d761eac62f 100644
--- a/src/quick/scenegraph/util/qsgtexture.cpp
+++ b/src/quick/scenegraph/util/qsgtexture.cpp
@@ -251,11 +251,15 @@ static void qt_debug_remove_texture(QSGTexture* texture)
 
     Specifies how the texture should treat texture coordinates.
 
-    \value Repeat Only the factional part of the texture coordiante is
+    \value Repeat Only the fractional part of the texture coordinate is
     used, causing values above 1 and below 0 to repeat.
 
     \value ClampToEdge Values above 1 are clamped to 1 and values
     below 0 are clamped to 0.
+
+    \value MirroredRepeat When the texture coordinate is even, only the
+    fractional part is used. When odd, the texture coordinate is set to
+    \c{1 - fractional part}. This value has been introduced in Qt 5.10.
  */
 
 /*!
@@ -550,7 +554,9 @@ void QSGTexture::updateBindOptions(bool force)
 
     if (force || d->wrapChanged) {
 #ifndef QT_NO_DEBUG
-        if (d->horizontalWrap == Repeat || d->verticalWrap == Repeat) {
+        if (d->horizontalWrap == Repeat || d->verticalWrap == Repeat
+            || d->horizontalWrap == MirroredRepeat || d->verticalWrap == MirroredRepeat)
+        {
             bool npotSupported = QOpenGLFunctions(QOpenGLContext::currentContext()).hasOpenGLFeature(QOpenGLFunctions::NPOTTextures);
             QSize size = textureSize();
             bool isNpot = !isPowerOfTwo(size.width()) || !isPowerOfTwo(size.height());
@@ -558,8 +564,18 @@ void QSGTexture::updateBindOptions(bool force)
                 qWarning("Scene Graph: This system does not support the REPEAT wrap mode for non-power-of-two textures.");
         }
 #endif
-        funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, d->horizontalWrap == Repeat ? GL_REPEAT : GL_CLAMP_TO_EDGE);
-        funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, d->verticalWrap == Repeat ? GL_REPEAT : GL_CLAMP_TO_EDGE);
+        GLenum wrapS = GL_CLAMP_TO_EDGE;
+        if (d->horizontalWrap == Repeat)
+            wrapS = GL_REPEAT;
+        else if (d->horizontalWrap == MirroredRepeat)
+            wrapS = GL_MIRRORED_REPEAT;
+        GLenum wrapT = GL_CLAMP_TO_EDGE;
+        if (d->verticalWrap == Repeat)
+            wrapT = GL_REPEAT;
+        else if (d->verticalWrap == MirroredRepeat)
+            wrapT = GL_MIRRORED_REPEAT;
+        funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, wrapS);
+        funcs->glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, wrapT);
         d->wrapChanged = false;
     }
 #else