Allow triangle fan in QSGGeometry when the underlying API supports it

Will not work with D3D and Metal. With those we will continue to reject
QSGGeometries having a drawing mode of DrawTrangineFan with a warning.

Relevant mainly for OpenGL and applications ported from Qt 5. For a
cross-platform, portable solution they would need to move away from
triangle fans, but in the meantime, if the intent is to function just
with OpenGL on Qt 6, it is good for compatibility if we enable this.

Change-Id: Iaa9376234ef854557458e5b6020e39c60666ad91
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
(cherry picked from commit 630e6db35d390b277d91f9cc7d392c8f50aef6c8)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 66ec7e688e67b8fb5879f56465bf8d5f4391318e)
(cherry picked from commit 27369d89c42cb1661ae104721d0048f6fbe2b82b)

2 files changed, 26 insertions, 12 deletions

diff --git a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
index d776f705e4..591d5d4df0 100644
--- a/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
+++ b/src/quick/scenegraph/coreapi/qsgbatchrenderer.cpp
@@ -174,7 +174,7 @@ QRhiCommandBuffer::IndexFormat qsg_indexFormat(const QSGGeometry *geometry)
     }
 }
 
-QRhiGraphicsPipeline::Topology qsg_topology(int geomDrawMode)
+QRhiGraphicsPipeline::Topology qsg_topology(int geomDrawMode, QRhi *rhi)
 {
     QRhiGraphicsPipeline::Topology topology = QRhiGraphicsPipeline::Triangles;
     switch (geomDrawMode) {
@@ -193,6 +193,20 @@ QRhiGraphicsPipeline::Topology qsg_topology(int geomDrawMode)
     case QSGGeometry::DrawTriangleStrip:
         topology = QRhiGraphicsPipeline::TriangleStrip;
         break;
+    case QSGGeometry::DrawTriangleFan:
+    {
+        static bool triangleFanSupported = false;
+        static bool triangleFanSupportChecked = false;
+        if (!triangleFanSupportChecked) {
+            triangleFanSupportChecked = true;
+            triangleFanSupported = rhi->isFeatureSupported(QRhi::TriangleFanTopology);
+        }
+        if (triangleFanSupported) {
+            topology = QRhiGraphicsPipeline::TriangleFan;
+            break;
+        }
+        Q_FALLTHROUGH();
+    }
     default:
         qWarning("Primitive topology 0x%x not supported", geomDrawMode);
         break;
@@ -2544,11 +2558,11 @@ void Renderer::updateClipState(const QSGClipNode *clipList, Batch *batch)
             if (firstStencilClipInBatch) {
                 m_stencilClipCommon.inputLayout.setBindings({ QRhiVertexInputBinding(g->sizeOfVertex()) });
                 m_stencilClipCommon.inputLayout.setAttributes({ QRhiVertexInputAttribute(0, 0, qsg_vertexInputFormat(*a), 0) });
-                m_stencilClipCommon.topology = qsg_topology(g->drawingMode());
+                m_stencilClipCommon.topology = qsg_topology(g->drawingMode(), m_rhi);
             }
 #ifndef QT_NO_DEBUG
             else {
-                if (qsg_topology(g->drawingMode()) != m_stencilClipCommon.topology)
+                if (qsg_topology(g->drawingMode(), m_rhi) != m_stencilClipCommon.topology)
                     qWarning("updateClipState: Clip list entries have different primitive topologies, this is not currently supported.");
                 if (qsg_vertexInputFormat(*a) != m_stencilClipCommon.inputLayout.cbeginAttributes()->format())
                     qWarning("updateClipState: Clip list entries have different vertex input layouts, this is must not happen.");
@@ -2740,7 +2754,7 @@ bool Renderer::ensurePipelineState(Element *e, const ShaderManager::Shader *sms,
         flags |= QRhiGraphicsPipeline::UsesStencilRef;
 
     ps->setFlags(flags);
-    ps->setTopology(qsg_topology(m_gstate.drawMode));
+    ps->setTopology(qsg_topology(m_gstate.drawMode, m_rhi));
     ps->setCullMode(m_gstate.cullMode);
     ps->setPolygonMode(m_gstate.polygonMode);
     ps->setMultiViewCount(m_gstate.multiViewCount);
diff --git a/src/quick/scenegraph/coreapi/qsgrhivisualizer.cpp b/src/quick/scenegraph/coreapi/qsgrhivisualizer.cpp
index d1f4e46ed0..a60d3a1984 100644
--- a/src/quick/scenegraph/coreapi/qsgrhivisualizer.cpp
+++ b/src/quick/scenegraph/coreapi/qsgrhivisualizer.cpp
@@ -22,7 +22,7 @@ namespace QSGBatchRenderer
 QMatrix4x4 qsg_matrixForRoot(Node *node);
 QRhiVertexInputAttribute::Format qsg_vertexInputFormat(const QSGGeometry::Attribute &a);
 QRhiCommandBuffer::IndexFormat qsg_indexFormat(const QSGGeometry *geometry);
-QRhiGraphicsPipeline::Topology qsg_topology(int geomDrawMode);
+QRhiGraphicsPipeline::Topology qsg_topology(int geomDrawMode, QRhi *rhi);
 
 RhiVisualizer::RhiVisualizer(Renderer *renderer)
     : Visualizer(renderer)
@@ -231,9 +231,9 @@ void RhiVisualizer::Fade::render(QRhiCommandBuffer *cb)
     cb->draw(4);
 }
 
-static void fillVertexIndex(RhiVisualizer::DrawCall *dc, QSGGeometry *g, bool withData, bool forceUintIndex)
+static void fillVertexIndex(RhiVisualizer::DrawCall *dc, QSGGeometry *g, bool withData, bool forceUintIndex, QRhi *rhi)
 {
-    dc->vertex.topology = qsg_topology(g->drawingMode());
+    dc->vertex.topology = qsg_topology(g->drawingMode(), rhi);
     dc->vertex.format = qsg_vertexInputFormat(g->attributes()[0]);
     dc->vertex.count = g->vertexCount();
     dc->vertex.stride = g->sizeOfVertex();
@@ -355,7 +355,7 @@ void RhiVisualizer::ChangeVis::gather(Node *n)
             qint32 projection = 0;
             memcpy(dc.uniforms.data + 148, &projection, 4);
 
-            fillVertexIndex(&dc, g, true, false);
+            fillVertexIndex(&dc, g, true, false, visualizer->m_renderer->m_rhi);
             drawCalls.append(dc);
         }
 
@@ -476,7 +476,7 @@ void RhiVisualizer::BatchVis::gather(Batch *b)
         QSGGeometryNode *gn = b->first->node;
         QSGGeometry *g = gn->geometry();
 
-        fillVertexIndex(&dc, g, false, forceUintIndex);
+        fillVertexIndex(&dc, g, false, forceUintIndex, visualizer->m_renderer->m_rhi);
 
         for (int ds = 0; ds < b->drawSets.size(); ++ds) {
             const DrawSet &set = b->drawSets.at(ds);
@@ -499,7 +499,7 @@ void RhiVisualizer::BatchVis::gather(Batch *b)
             QMatrix4x4 m = matrix * *gn->matrix();
             memcpy(dc.uniforms.data, m.constData(), 64);
 
-            fillVertexIndex(&dc, g, false, forceUintIndex);
+            fillVertexIndex(&dc, g, false, forceUintIndex, visualizer->m_renderer->m_rhi);
 
             dc.buf.vbuf = b->vbo.buf;
             dc.buf.vbufOffset = vOffset;
@@ -591,7 +591,7 @@ void RhiVisualizer::ClipVis::gather(QSGNode *node)
             memcpy(dc.uniforms.data + 144, &pattern, 4);
             qint32 projection = 0;
             memcpy(dc.uniforms.data + 148, &projection, 4);
-            fillVertexIndex(&dc, g, true, false);
+            fillVertexIndex(&dc, g, true, false, visualizer->m_renderer->m_rhi);
             drawCalls.append(dc);
         }
     }
@@ -703,7 +703,7 @@ void RhiVisualizer::OverdrawVis::gather(Node *n)
             qint32 projection = 1;
             memcpy(dc.uniforms.data + 148, &projection, 4);
 
-            fillVertexIndex(&dc, g, true, false);
+            fillVertexIndex(&dc, g, true, false, visualizer->m_renderer->m_rhi);
             drawCalls.append(dc);
         }
     }