Hi all, I wanted to share an update on the progress of my GSoC project - reworking the Impress slideshow rendering that currently uses GDIMetafiles with a primitive-based rendering approach.
The existing system takes drawinglayer primitives, converts them into a metafile, and then renders that using the XCanvas interface. XCanvas itself is abstract and gets wrapped inside cppcanvas, with cairocanvas (on Linux) handling the actual rendering. Essentially, we’re converting from primitives -> metafile -> XCanvas -> screen. Initially, I planned to write a new primitive renderer that directly targets the XCanvas interface. But after discussions with my mentor, we decided to try stripping out the hacks - removing the detour through metafiles and cppcanvas - and instead aim for rendering primitives directly to screen. Since drawinglayer already has several pixel processors (like CairoPixelProcessor2D), this path looks promising. Summary of Code Understanding - Internal Structure of Shapes and Primitives - I investigated how DrawShape relates to shape metadata. - Shapes reference SvxShape, which internally maps to SdrObject. - SdrObject connects to ViewContact, which generates Primitive2DContainer through createViewIndependentPrimitive2DSequence(). Understanding SlideImpl::loadShapes() - I traced through SlideImpl::loadShapes() (called from implPrefetchShow) to see how shapes get imported. - There are two ShapeImporter functors (master‐page vs. normal page). Both push XShapesEntry objects onto maShapesStack. Figured Out Where Metafiles Are Generated - The DrawShape gets its metafile using UnoGraphicExporter. - Under the hood, a primitives-to-metafile renderer is used to generate metafiles. Tracing the Rendering Pipeline - SlideImpl::show() triggers the rendering. - The rendering path calls slideRenderer(), which in turn calls SlideImpl::getCurrentSlideBitmap(), and if necessary, createCurrentSlideBitmap(). - During bitmap creation, shapes are rendered to a BitmapCanvas that shares its underlying Cairo surface with the SpriteCanvas (verified via GDB inspection). - LayerManager::renderTo(...) iterates over all DrawShape instances, temporarily attaches a DummyLayer for each, and calls pShape->addViewLayer(...), which uses the metafile renderer to render onto the target bitmap canvas. Exploring Animation & Sprites - I backtraced ActivityImpl::ActivityImpl, used for text-based intrinsic animations. - I reviewed the animation frame updates via SlideShowImpl::update(), which repeatedly calls maActivitiesQueue.process(). - Activities are implemented as subclasses like SimpleActivity, which execute frame updates via animation functors (e.g., PathAnimation) that manipulate shape properties over time. - The final frame rendering goes through LayerManager::update() and ViewShape::update(). Since the current code depends a lot on XCanvas, I’ll proceed iteratively - removing the extra layers and moving toward rendering primitives directly to the screen. That’s it for now. I’ll continue posting updates as the work progresses. Best, Shardul
