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James Gregory 2013-12-30 18:34:31 +11:00
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67-04.md
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@ -3,7 +3,7 @@
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By the same token, Listing 67.1 is quite a bit more complicated than the
earlier code. The earlier code’s HSR consisted of a z-sort of objects,
earlier code. The earlier code's HSR consisted of a z-sort of objects,
followed by the drawing of the objects in back-to-front order, one
polygon at a time. Apart from the simple object sorter, all that was
needed was backface culling and a polygon rasterizer.
@ -13,16 +13,16 @@ process. After backface culling, the edges of each of the polygons in
the scene are added to the global edge list, by way of
**AddPolygonEdges()**. After all edges have been added, the edges are
turned into spans by **ScanEdges()**, with each pixel on the screen
being covered by one and only one span (that is, there’s no overdraw).
Once all the spans have been generated, they’re drawn by
being covered by one and only one span (that is, there's no overdraw).
Once all the spans have been generated, they're drawn by
**DrawSpans()**, and rasterization is complete.
There’s nothing tricky about **AddPolygonEdges()**, and **DrawSpans()**,
There's nothing tricky about **AddPolygonEdges()**, and **DrawSpans()**,
as implemented in Listing 67.1, is very straightforward as well. In an
implementation that supported texture mapping, however, all the spans
wouldn’t be put on one global span list and drawn at once, as is done in
wouldn't be put on one global span list and drawn at once, as is done in
Listing 67.1, because that would result in drawing spans from all the
surfaces in no particular order. (A surface is a drawing object that’s
surfaces in no particular order. (A surface is a drawing object that's
originally described by a polygon, but in **ScanEdges()** there is no
polygon in the classic sense of a set of vertices bounding an area, but
rather just a set of edges and a surface that describes how to draw the
@ -81,7 +81,7 @@ leading edge causes its surface to be 1/z-sorted into the surface stack,
with a span emitted if necessary. Each trailing edge causes its surface
to be removed from the surface stack, again with a span emitted if
necessary. As you can see from Listing 67.1, it takes a fair bit of code
to implement this, but all that’s really going on is a surface stack
to implement this, but all that's really going on is a surface stack
driven by edge events.
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