53 lines
1.7 KiB
C
53 lines
1.7 KiB
C
//---
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//
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// gint drawing module: display
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//
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// Handles vram manipulation and drawing.
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//
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//
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// :: Rectangle masks
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//
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// The concept of 'rectangle masks' is used several times in this module.
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// It is based on the fact that an operation that affects a rectangle acts
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// the same on all its lines. Therefore the behavior of the operation is
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// determined by its behavior on a single line, which is represented using
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// 'masks' whose bits indicate whether a pixel is affected (1) or not (0).
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//
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// For example when clearing the screen rectangle (16, 16, 112, 48), the
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// masks will represent information '16 to 112 on x-axis', and will hold
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// the following values : 0000ffff, ffffffff, ffffffff and ffff0000. These
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// masks can then be used by setting vram[offset] &= ~masks[i]. This
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// appears to be very flexible : for instance, vram[offset] ^= masks[i]
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// will reverse the pixels in the same rectangle.
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//
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// This technique can also be used in more subtle cases with more complex
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// patterns, but within this module it is unlikely to happen.
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//
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//---
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#ifndef _DISPLAY_INTERNALS_H
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#define _DISPLAY_INTERNALS_H
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extern int *vram;
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/*
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adjustRectangle()
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Adjusts the given rectangle coordinates to ensure that :
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- the rectangle is entirely contained in the screen
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- x1 < x2
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- y1 < y2
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which is needed when working with screen rectangles.
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*/
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static void adjustRectangle(int *x1, int *y1, int *x2, int *y2);
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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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static void getMasks(int x1, int x2, unsigned int *masks);
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#endif // _DISPLAY_INTERNALS_H
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