rhi: Add depth bias and slope scaled depth bias

Beware of the API terminology: GL 'factor' = 'slope scaled depth bias',
GL 'units' = '(constant) depth bias'.

Task-number: QTBUG-81843
Change-Id: I03e3618d007cbf7100add0de4950a6163d788cc7
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

6 files changed, 37 insertions, 1 deletions

diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index e32fc0f4a0..d17112a241 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -1155,6 +1155,12 @@ public:
     float lineWidth() const { return m_lineWidth; }
     void setLineWidth(float width) { m_lineWidth = width; }
 
+    int depthBias() const { return m_depthBias; }
+    void setDepthBias(int bias) { m_depthBias = bias; }
+
+    float slopeScaledDepthBias() const { return m_slopeScaledDepthBias; }
+    void setSlopeScaledDepthBias(float bias) { m_slopeScaledDepthBias = bias; }
+
     void setShaderStages(std::initializer_list<QRhiShaderStage> list) { m_shaderStages = list; }
     template<typename InputIterator>
     void setShaderStages(InputIterator first, InputIterator last)
@@ -1193,6 +1199,8 @@ protected:
     quint32 m_stencilWriteMask = 0xFF;
     int m_sampleCount = 1;
     float m_lineWidth = 1.0f;
+    int m_depthBias = 0;
+    float m_slopeScaledDepthBias = 0.0f;
     QVarLengthArray<QRhiShaderStage, 4> m_shaderStages;
     QRhiVertexInputLayout m_vertexInputLayout;
     QRhiShaderResourceBindings *m_shaderResourceBindings = nullptr;
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index ec86c31719..75b90b6995 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -3467,6 +3467,8 @@ bool QD3D11GraphicsPipeline::build()
     rastDesc.FillMode = D3D11_FILL_SOLID;
     rastDesc.CullMode = toD3DCullMode(m_cullMode);
     rastDesc.FrontCounterClockwise = m_frontFace == CCW;
+    rastDesc.DepthBias = m_depthBias;
+    rastDesc.SlopeScaledDepthBias = m_slopeScaledDepthBias;
     rastDesc.DepthClipEnable = true;
     rastDesc.ScissorEnable = m_flags.testFlag(UsesScissor);
     rastDesc.MultisampleEnable = rhiD->effectiveSampleCount(m_sampleCount).Count > 1;
diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index 2620cc4d7b..62f808ce81 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -2386,7 +2386,14 @@ void QRhiGles2::executeBindGraphicsPipeline(QRhiGraphicsPipeline *ps)
         f->glDisable(GL_STENCIL_TEST);
     }
 
-    if (psD->topology() == QRhiGraphicsPipeline::Lines || psD->topology() == QRhiGraphicsPipeline::LineStrip)
+    if (psD->m_depthBias != 0 || !qFuzzyIsNull(psD->m_slopeScaledDepthBias)) {
+        f->glPolygonOffset(psD->m_slopeScaledDepthBias, psD->m_depthBias);
+        f->glEnable(GL_POLYGON_OFFSET_FILL);
+    } else {
+        f->glDisable(GL_POLYGON_OFFSET_FILL);
+    }
+
+    if (psD->m_topology == QRhiGraphicsPipeline::Lines || psD->m_topology == QRhiGraphicsPipeline::LineStrip)
         f->glLineWidth(psD->m_lineWidth);
 
     f->glUseProgram(psD->program);
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index 053061bddf..9e8f1ac096 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -298,6 +298,8 @@ struct QMetalGraphicsPipelineData
     MTLPrimitiveType primitiveType;
     MTLWinding winding;
     MTLCullMode cullMode;
+    float depthBias;
+    float slopeScaledDepthBias;
     QMetalShader vs;
     QMetalShader fs;
 };
@@ -956,6 +958,14 @@ void QRhiMetal::setGraphicsPipeline(QRhiCommandBuffer *cb, QRhiGraphicsPipeline
             [cbD->d->currentRenderPassEncoder setFrontFacingWinding: psD->d->winding];
             cbD->currentFrontFaceWinding = int(psD->d->winding);
         }
+        if (!qFuzzyCompare(psD->d->depthBias, cbD->currentDepthBiasValues.first)
+                || !qFuzzyCompare(psD->d->slopeScaledDepthBias, cbD->currentDepthBiasValues.second))
+        {
+            [cbD->d->currentRenderPassEncoder setDepthBias: psD->d->depthBias
+                                                            slopeScale: psD->d->slopeScaledDepthBias
+                                                            clamp: 0.0f];
+            cbD->currentDepthBiasValues = { psD->d->depthBias, psD->d->slopeScaledDepthBias };
+        }
     }
 
     psD->lastActiveFrameSlot = currentFrameSlot;
@@ -3454,6 +3464,8 @@ bool QMetalGraphicsPipeline::build()
     d->primitiveType = toMetalPrimitiveType(m_topology);
     d->winding = m_frontFace == CCW ? MTLWindingCounterClockwise : MTLWindingClockwise;
     d->cullMode = toMetalCullMode(m_cullMode);
+    d->depthBias = float(m_depthBias);
+    d->slopeScaledDepthBias = m_slopeScaledDepthBias;
 
     lastActiveFrameSlot = -1;
     generation += 1;
@@ -3602,6 +3614,7 @@ void QMetalCommandBuffer::resetPerPassCachedState()
     currentIndexFormat = QRhiCommandBuffer::IndexUInt16;
     currentCullMode = -1;
     currentFrontFaceWinding = -1;
+    currentDepthBiasValues = { 0.0f, 0.0f };
 
     d->currentFirstVertexBinding = -1;
     d->currentVertexInputsBuffers.clear();
diff --git a/src/gui/rhi/qrhimetal_p_p.h b/src/gui/rhi/qrhimetal_p_p.h
index 24f3340db1..58e93e2cdb 100644
--- a/src/gui/rhi/qrhimetal_p_p.h
+++ b/src/gui/rhi/qrhimetal_p_p.h
@@ -288,6 +288,7 @@ struct QMetalCommandBuffer : public QRhiCommandBuffer
     QRhiCommandBuffer::IndexFormat currentIndexFormat;
     int currentCullMode;
     int currentFrontFaceWinding;
+    QPair<float, float> currentDepthBiasValues;
 
     const QRhiNativeHandles *nativeHandles();
     void resetState();
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index cf6f14368c..e41a321637 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -6208,6 +6208,11 @@ bool QVkGraphicsPipeline::build()
     rastInfo.sType = VK_STRUCTURE_TYPE_PIPELINE_RASTERIZATION_STATE_CREATE_INFO;
     rastInfo.cullMode = toVkCullMode(m_cullMode);
     rastInfo.frontFace = toVkFrontFace(m_frontFace);
+    if (m_depthBias != 0 || !qFuzzyIsNull(m_slopeScaledDepthBias)) {
+        rastInfo.depthBiasEnable = true;
+        rastInfo.depthBiasConstantFactor = float(m_depthBias);
+        rastInfo.depthBiasSlopeFactor = m_slopeScaledDepthBias;
+    }
     rastInfo.lineWidth = rhiD->hasWideLines ? m_lineWidth : 1.0f;
     pipelineInfo.pRasterizationState = &rastInfo;