Creates a new sub-context which maps to a part of an existing context.
The coordinate arguments (x1 through y2) are interpreted relative to the parent context's limits. Pixel addressing is zero-based even in sub-contexts, i.e. the address of the top left pixel is (0,0) even in a sub-context which has been mapped onto the interior of its parent context.
x1 |
the left bounds |
y1 |
the top bounds |
x2 |
the right bounds |
y2 |
the bottom bounds |
parent |
the parent context or null to use the screen |
where |
an unused Context struct to hold the subcontext or null |
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