This driver allows access to a Client Image, an imaged based in RGB colors with 24 or 32 bits per pixel (8 per channel). It is used to implement high-quality off-screen drawings, but is slower than the Server Image version. In fact, it is a rasterizer, that is, it converts vector primitives into a raster representation. All primitives are implemented by the library and are not system-dependent (the primitives of the Server Image version are system-dependent).
The canvas is created by means of a call to the function cdCreateCanvas(CD_IMAGERGB, Data), after which other functions in the CD library can be called as usual. The function creates an RGB image, and then a CD canvas. The Data parameter string has the following format:
"widthxheight [r g b] -r[resolution]" in C "%dx%d %p %p %p -r%g" or "widthxheight [r g b a] -r[resolution] -a" in C "%dx%d %p %p %p %p -r%g -a"
It must include the canvas' dimensions. Width and height are provided in pixels (note the lowercase "x" between them). If width or height are 0 then 1 will be used. As an option, you can specify the buffers to be used by the driver, so that you can draw over an existing image, [r g b] or [r g b a] are pointers to the component buffer, just like PutImageRectRGB/A. The resolution can be defined with parameter -r; its default value is "3.78 pixels/mm" (96 DPI).
When the parameter -a is specified an alpha channel will be added to the canvas underlying image. All primitives will be composed using an over operator if the foreground or background colors have alpha components. This channel is initialized with transparent (0). The other channels are initialized with white (255, 255, 255). After drawing in the RGBA image the resulting alpha channel can be used to compose the image in another canvas.
All channels are initialized only when allocated internally by the driver. They are not initialized when allocated by the application.
Any amount of such canvases may exist simultaneously. It is important to note that a call to function cdKillCanvas is required to release internal allocated memory.
In Lua, the canvas can be created in two ways: with an already defined image or without it. With an image, an RGB image must be passed as parameter instead of the string, created by functions cd.CreateImageRGB, cd.CreateImageRGBA or cd.CreateBitmap in Lua. The resolution must be passed in a second parameter after the image.
Returns the canvas' internal image.
This drivers depends on the Simulation driver. But the functions bellow behave differently.