rlottie/vector: support subsurface rendering with arbitrary offset.

src/lottie/lottieitem.cpp

@@ -126,16 +126,20 @@ bool LOTCompItem::render(const rlottie::Surface &surface)
                    surface.width(), surface.height(),
                    surface.bytesPerLine(), VBitmap::Format::ARGB32_Premultiplied);
 
+
     /* schedule all preprocess task for this frame at once.
      */
     mDrawableList.clear();
     mRootLayer->renderList(mDrawableList);
-    VRect clip(0, 0, surface.width(), surface.height());
+    VRect clip(0, 0, surface.drawRegionWidth(), surface.drawRegionHeight());
     for (auto &e : mDrawableList) {
         e->preprocess(clip);
     }
 
     VPainter painter(&bitmap);
+    // set sub surface area for drawing.
+    painter.setDrawRegion(VRect(surface.drawRegionPosX(), surface.drawRegionPosY(),
+                          surface.drawRegionWidth(), surface.drawRegionHeight()));
     mRootLayer->render(&painter, {}, {});
 
     return true;

src/vector/vdrawhelper.cpp

@@ -207,7 +207,7 @@ VBitmap::Format VRasterBuffer::prepare(VBitmap *image)
 void VSpanData::init(VRasterBuffer *image)
 {
     mRasterBuffer = image;
-    mSystemClip = VRect(0, 0, image->width(), image->height());
+    setDrawRegion(VRect(0, 0, image->width(), image->height()));
     mType = VSpanData::Type::None;
     mBlendFunc = nullptr;
     mUnclippedBlendFunc = nullptr;

src/vector/vdrawhelper.h

@@ -150,15 +150,21 @@ struct VSpanData {
                 VPainter::CompositionMode mode = VPainter::CompModeSrcOver,
                 int                       alpha = 255);
     void  setupMatrix(const VMatrix &matrix);
-    void  setPos(const VPoint &pos) { mPos = pos; }
+
     VRect clipRect() const
     {
-        return mSystemClip.translated(-mPos.x(), -mPos.y());
+        return VRect(0, 0, mDrawableSize.width(), mDrawableSize.height());
+    }
+
+    void setDrawRegion(const VRect &region)
+    {
+        mOffset = VPoint(region.left(), region.top());
+        mDrawableSize = VSize(region.width(), region.height());
     }
 
     uint *buffer(int x, int y) const
     {
-        return (uint *)(mRasterBuffer->scanLine(y + mPos.y())) + x + mPos.x();
+        return (uint *)(mRasterBuffer->scanLine(y + mOffset.y())) + x + mOffset.x();
     }
     void initTexture(const VBitmap *image, int alpha, VBitmapData::Type type, const VRect &sourceRect);
 
@@ -166,10 +172,10 @@ struct VSpanData {
     VRasterBuffer *                      mRasterBuffer;
     ProcessRleSpan                       mBlendFunc;
     ProcessRleSpan                       mUnclippedBlendFunc;
-    VRect                                mSystemClip;
     VSpanData::Type                      mType;
     std::shared_ptr<VSpanData::Pinnable> mCachedGradient;
-    VPoint                               mPos;
+    VPoint                               mOffset; // offset to the subsurface
+    VSize                                mDrawableSize;// suburface size
     union {
         uint32_t      mSolid;
         VGradientData mGradient;

src/vector/vpainter.cpp

@@ -32,15 +32,13 @@ public:
     VSpanData     mSpanData;
 };
 
-void VPainterImpl::drawRle(const VPoint &pos, const VRle &rle)
+void VPainterImpl::drawRle(const VPoint &, const VRle &rle)
 {
     if (rle.empty()) return;
     // mSpanData.updateSpanFunc();
 
     if (!mSpanData.mUnclippedBlendFunc) return;
 
-    mSpanData.setPos(pos);
-
     // do draw after applying clip.
     rle.intersect(mSpanData.clipRect(), mSpanData.mUnclippedBlendFunc,
                   &mSpanData);
@@ -61,9 +59,9 @@ static void fillRect(const VRect &r, VSpanData *data)
     int x1, x2, y1, y2;
 
     x1 = std::max(r.x(), 0);
-    x2 = std::min(r.x() + r.width(), data->mRasterBuffer->width());
+    x2 = std::min(r.x() + r.width(), data->mDrawableSize.width());
     y1 = std::max(r.y(), 0);
-    y2 = std::min(r.y() + r.height(), data->mRasterBuffer->height());
+    y2 = std::min(r.y() + r.height(), data->mDrawableSize.height());
 
     if (x2 <= x1 || y2 <= y1)
         return;
@@ -130,6 +128,12 @@ bool VPainter::begin(VBitmap *buffer)
 }
 void VPainter::end() {}
 
+void  VPainter::setDrawRegion(const VRect &region)
+{
+    mImpl->mSpanData.setDrawRegion(region);
+}
+
+
 void VPainter::setBrush(const VBrush &brush)
 {
     mImpl->mSpanData.setup(brush);
@@ -153,7 +157,7 @@ void VPainter::drawRle(const VRle &rle, const VRle &clip)
 
 VRect VPainter::clipBoundingRect() const
 {
-    return mImpl->mSpanData.mSystemClip;
+    return mImpl->mSpanData.clipRect();
 }
 
 void  VPainter::drawBitmap(const VPoint &point, const VBitmap &bitmap, const VRect &source)

src/vector/vpainter.h

@@ -40,6 +40,7 @@ public:
     VPainter(VBitmap *buffer);
     bool  begin(VBitmap *buffer);
     void  end();
+    void  setDrawRegion(const VRect &region); // sub surface rendering area.
     void  setBrush(const VBrush &brush);
     void  setCompositionMode(CompositionMode mode);
     void  drawRle(const VPoint &pos, const VRle &rle);