Fix SVG texture color banding (#4891)

Author: Zephkek

Client/core/Graphics/CGraphics.cpp

@@ -1080,6 +1080,10 @@ void CGraphics::DrawMaterialPrimitiveQueued(std::vector<PrimitiveMaterialVertice
     sDrawQueueItem Item;
     Item.eType = QUEUE_PRIMITIVEMATERIAL;
     Item.blendMode = m_ActiveBlendMode;
+    // Same PM auto-route as DrawTextureQueued, so dxDrawMaterialPrimitive
+    // composites SVG (premultiplied) textures correctly under default blend.
+    if (Item.blendMode == EBlendMode::BLEND && pMaterial && pMaterial->m_bPremultipliedAlpha)
+        Item.blendMode = EBlendMode::ADD;
     Item.PrimitiveMaterial.eType = eType;
     Item.PrimitiveMaterial.pMaterial = pMaterial;
     Item.PrimitiveMaterial.pVecVertices = pVecVertices;
@@ -1134,6 +1138,11 @@ void CGraphics::DrawTextureQueued(float fX, float fY, float fWidth, float fHeigh
     // Set up a queue item
     sDrawQueueItem Item;
     Item.blendMode = m_ActiveBlendMode;
+    // Premultiplied-alpha textures (SVG) need the (ONE, INVSRCALPHA) pipeline,
+    // not the straight-alpha BLEND mode. Route the default blend to ADD when
+    // the script hasn't asked for a specific mode (issue #4891).
+    if (Item.blendMode == EBlendMode::BLEND && pMaterial && pMaterial->m_bPremultipliedAlpha)
+        Item.blendMode = EBlendMode::ADD;
     Item.Texture.fX = fX;
     Item.Texture.fY = fY;
     Item.Texture.fWidth = fWidth;

Client/core/Graphics/CRenderItem.VectorGraphic.cpp

@@ -24,6 +24,9 @@ void CVectorGraphicItem::PostConstruct(CRenderItemManager* pManager, uint width,
     m_uiSizeY = height;
     m_uiSurfaceSizeX = width;
     m_uiSurfaceSizeY = height;
+    // lunasvg writes premultiplied ARGB into the surface; let the draw
+    // path use a PM-aware blend instead of unpremultiplying per pixel.
+    m_bPremultipliedAlpha = true;
 
     CreateUnderlyingData();
 }

Client/mods/deathmatch/logic/CClientVectorGraphicDisplay.cpp

@@ -56,37 +56,6 @@ void CClientVectorGraphicDisplay::Render()
     }
 }
 
-void CClientVectorGraphicDisplay::UnpremultiplyBitmap(Bitmap& bitmap)
-{
-    auto width = bitmap.width();
-    auto height = bitmap.height();
-    auto stride = bitmap.stride();
-    auto rowData = bitmap.data();
-
-    for (decltype(height) y = 0; y < height; y++)
-    {
-        auto data = rowData;
-        for (decltype(width) x = 0; x < width; x++)
-        {
-            auto& b = data[0];
-            auto& g = data[1];
-            auto& r = data[2];
-            auto& a = data[3];
-
-            if (a != 0)
-            {
-                r = (r * 255) / a;
-                g = (g * 255) / a;
-                b = (b * 255) / a;
-            }
-
-            data += 4;
-        }
-
-        rowData += stride;
-    }
-}
-
 void CClientVectorGraphicDisplay::UpdateTexture()
 {
     if (!m_pVectorGraphic || m_pVectorGraphic->IsDestroyed())
@@ -144,7 +113,10 @@ void CClientVectorGraphicDisplay::UpdateTexture()
             return;
         }
 
-        UnpremultiplyBitmap(bitmap);
+        // The surface stays in lunasvg's native premultiplied ARGB layout.
+        // CGraphics::DrawTextureQueued routes the draw to a PM blend so we
+        // avoid the precision loss caused by an integer unpremultiply
+        // (see issue #4891 banding on translucent SVG gradients).
 
         // Unlock surface
         surface->UnlockRect();

Client/mods/deathmatch/logic/CClientVectorGraphicDisplay.h

@@ -36,8 +36,6 @@ class CClientVectorGraphicDisplay final : public CClientDisplay
     void Update();
 
 private:
-    void UnpremultiplyBitmap(lunasvg::Bitmap& bitmap);
-
     CClientVectorGraphic* m_pVectorGraphic;
 
     bool m_bIsCleared;

Client/sdk/core/CRenderItemManagerInterface.h

@@ -351,12 +351,17 @@ class CEffectWrap : public CRenderItem
 class CMaterialItem : public CRenderItem
 {
     DECLARE_CLASS(CMaterialItem, CRenderItem)
-    CMaterialItem() : ClassInit(this), m_TextureAddress(TADDRESS_WRAP), m_uiBorderColor(0) {}
+    CMaterialItem() : ClassInit(this), m_TextureAddress(TADDRESS_WRAP), m_uiBorderColor(0), m_bPremultipliedAlpha(false) {}
 
     uint            m_uiSizeX;
     uint            m_uiSizeY;
     ETextureAddress m_TextureAddress;
     uint            m_uiBorderColor;
+    // True if the texture pixels are stored with premultiplied alpha. When set,
+    // the default dxDrawImage blend ("blend") is internally routed through the
+    // (ONE, INVSRCALPHA) pipeline so compositing is mathematically correct
+    // without losing precision to a per-pixel integer unpremultiply.
+    bool            m_bPremultipliedAlpha;
 };
 
 ////////////////////////////////////////////////////////////////