35 lines
1.1 KiB
C
35 lines
1.1 KiB
C
#include <display_internals.h>
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/*
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getMasks()
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Computes the rectangle masks needed to affect pixels located between x1
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and x2 (both included). The four masks are stored in the third argument
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(seen as an array).
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See this module's internals header file for more information.
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*/
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void getMasks(int x1, int x2, unsigned int *masks)
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{
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// Indexes of the first and last longs that are non-blank.
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int l1 = x1 >> 5;
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int l2 = x2 >> 5;
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int i = 0;
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// Setting the base masks. Those are the final values, except for the
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// longs with indexes l1 and l2, that still need to be adjusted.
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while(i < l1) masks[i++] = 0x00000000;
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while(i <= l2) masks[i++] = 0xffffffff;
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while(i < 4) masks[i++] = 0x00000000;
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// Removing the long number information in x1 and x2 (that is, the
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// multiples of 32) to keep only the interesting information -- the
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// number of null bits to add in l1 and l2.
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x1 &= 31;
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// Inverting x2 is here the same as computing 32 - x, since 32 is a
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// power of 2 (positive bits at the left are removed by the mask).
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x2 = ~x2 & 31;
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// Setting the first and last masks.
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masks[l1] &= (0xffffffff >> x1);
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masks[l2] &= (0xffffffff << x2);
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}
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