NEC uPD72257, Preliminary User'S Manual

Page: 238 / 343

Consider the last case:
In this case the triangle has to be splitted and rendered as two parts for the
spanstore optimization to work.
It is also possible to delay spanstore activation for a number of lines. This is used
by the driver with circles:
In this case the spanstore would not be activated in the top left corner but in the
bottom left corner.
The top right and the bottom left empty corner would not be rasterized because
of the spanabort optimization.
8.5.8.2 Spanabort
The second optimization assumes that the object that has to be drawn is convex.
This means there is only one span per scanline to be drawn. A non convex object
would be e.g. a triangle that is not filled and just consists of a thick border.
In case of a convex object the rasterization can be stopped in case the end of the
first span is detected.
This optimization has no other complications in case of convex objects.
Chapter 8 Drawing Engine
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Preliminary User's Manual S19203EE1V3UM00