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diff --git a/drawinglayer/README.md b/drawinglayer/README.md new file mode 100644 index 000000000000..b530ba6fedac --- /dev/null +++ b/drawinglayer/README.md @@ -0,0 +1,85 @@ +Drawing API that can specify what to draw via a kind of display list. + +Example of the DrawingLayer use is eg. in svx/source/xoutdev/xtabhtch.cxx:121. +A stripped down version with extended comments: + + // Create a hatch primitive (here a rectangle that will be filled with + // the appropriate hatching, but has no border). + // This will not draw it yet; it's so far only constructed to add it to a + // display list later. + const drawinglayer::primitive2d::Primitive2DReference aHatchPrimitive( + new drawinglayer::primitive2d::PolyPolygonHatchPrimitive2D(...)); + + // Create a rectangle around the hatch, to give it a border. + const drawinglayer::primitive2d::Primitive2DReference aBlackRectanglePrimitive( + new drawinglayer::primitive2d::PolygonHairlinePrimitive2D(...)); + + // Here we want to render to a virtual device (to later obtain the bitmap + // out of that), so prepare it. + VirtualDevice aVirtualDevice; + + // Create processor and draw primitives, to get it ready for rendering. + std::unique_ptr<drawinglayer::processor2d::BaseProcessor2D> pProcessor2D( + drawinglayer::processor2d::createPixelProcessor2DFromOutputDevice(...)); + + if (pProcessor2D) + { + // Fill-in the display list. + drawinglayer::primitive2d::Primitive2DSequence aSequence(2); + + aSequence[0] = aHatchPrimitive; + aSequence[1] = aBlackRectanglePrimitive; + + // Render it to the virtual device. + pProcessor2D->process(aSequence); + pProcessor2D.reset(); + } + + // Obtain the bitmap that was rendered from the virtual device, to re-use + // it in the widget. + aRetval = aVirtualDevice.GetBitmap(Point(0, 0), aVirtualDevice.GetOutputSizePixel()); + +== DrawingLayer glossary == + +Primitives - classes that represent what should be drawn. It holds the data +what to draw, but does not contain any kind of the rendering. Some of the +primitives are 'Basic primitives', that are primitives that cannot be +decomposed. The rest of the primitives can be decomposed to the basic +primitives. + +Decomposition - a way how to break down the more complicated primitives into +the basic primitives, and represent them via them; this logically makes the +plain Primitive2DSequence display list a hierarchy. +Eg. PolygonMarkerPrimitive2D can be decomposed to 2 hairlines +PolyPolygonHairlinePrimitive2D's, each with different color. + +Processor - a class that goes through the hierarchy of the Primitives, and +renders it some way. Various processors, like VclPixelProcessor2D (renders to +the screen), VclMetafileProcessor2D (renders to the VCL metafile, eg. for +printing), etc. + +== How to Implement a new Primitive ("something new to draw") == + +* Create an ancestor of BasePrimitive2D + (or of its ancestor if it fits the purpose better) + + * Assign it an ID [in drawinglayer_primitivetypes2d.hxx] + + * Implement its decomposition + [virtual Primitive2DSequence create2DDecomposition(...)] + +* Extend the (various) processor(s) + If you need more than relying on just the decomposition + +== Where is DrawingLayer used == + +* SdrObject(s) (rectangles, Circles, predefined shapes etc.) + +* Selections + +* Various smaller cases to 'just draw something' + + * Draw to a virtual device, and use the resulting bitmap (like the example + above) + +* Custom widgets (like the Header / Footer indicator button) |