1drawing_mode(3)                 Allegro manual                 drawing_mode(3)
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NAME

6       drawing_mode - Sets the graphics drawing mode. Allegro game programming
7       library.
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SYNOPSIS

10       #include <allegro.h>
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13       void  drawing_mode(int  mode,  BITMAP  *pattern,  int   x_anchor,   int
14       y_anchor);
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DESCRIPTION

17       Sets  the  graphics  drawing mode. This only affects the geometric rou‐
18       tines like putpixel, lines, rectangles, circles,  polygons,  floodfill,
19       etc,  not  the  text output, blitting, or sprite drawing functions. The
20       mode should be one of the following constants:
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22          DRAW_MODE_SOLID               - the default, solid color
23                                          drawing
24          DRAW_MODE_XOR                 - exclusive-or drawing
25          DRAW_MODE_COPY_PATTERN        - multicolored pattern fill
26          DRAW_MODE_SOLID_PATTERN       - single color pattern fill
27          DRAW_MODE_MASKED_PATTERN      - masked pattern fill
28          DRAW_MODE_TRANS               - translucent color blending
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30       In DRAW_MODE_SOLID, pixels of the bitmap being drawn  onto  are  simply
31       replaced by those produced by the drawing function.
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33       In DRAW_MODE_XOR, pixels are written to the bitmap with an exclusive-or
34       operation rather than a simple copy, so drawing the  same  shape  twice
35       will  erase it. Because it involves reading as well as writing the bit‐
36       map memory, xor drawing is a lot slower than the normal replace mode.
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38       With the patterned modes, you provide a pattern bitmap which  is  tiled
39       across  the surface of the shape. Allegro stores a pointer to this bit‐
40       map rather than copying it, so you must not destroy the bitmap while it
41       is  still  selected as the pattern. The width and height of the pattern
42       must be powers of two, but they can be different, eg. a  64x16  pattern
43       is fine, but a 17x3 one is not. The pattern is tiled in a grid starting
44       at point (x_anchor, y_anchor). Normally you should just pass  zero  for
45       these  values, which lets you draw several adjacent shapes and have the
46       patterns meet up exactly along the shared  edges.  Zero  alignment  may
47       look  peculiar  if  you are moving a patterned shape around the screen,
48       however, because the shape will move but  the  pattern  alignment  will
49       not, so in some situations you may wish to alter the anchor position.
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51       When  you  select DRAW_MODE_COPY_PATTERN, pixels are simply copied from
52       the pattern bitmap onto the destination bitmap. This allows the use  of
53       multicolored patterns, and means that the color you pass to the drawing
54       routine is ignored. This is the fastest of the patterned modes.
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56       In DRAW_MODE_SOLID_PATTERN, each pixel in the pattern  bitmap  is  com‐
57       pared  with  the mask color, which is zero in 256-color modes or bright
58       pink for truecolor data (maximum red and blue, zero green). If the pat‐
59       tern  pixel  is  solid,  a pixel of the color you passed to the drawing
60       routine is written to the destination bitmap, otherwise a zero is writ‐
61       ten.  The  pattern  is thus treated as a monochrome bitmask, which lets
62       you use the same pattern to draw different shapes in different  colors,
63       but prevents the use of multicolored patterns.
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65       DRAW_MODE_MASKED_PATTERN is almost the same as DRAW_MODE_SOLID_PATTERN,
66       but the masked pixels are skipped rather than being written  as  zeros,
67       so the background shows through the gaps.
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69       In  DRAW_MODE_TRANS,  the  global  color_map table or truecolor blender
70       functions are used to overlay pixels on top of the existing image. This
71       must  only  be  used after you have set up the color mapping table (for
72       256 color modes) or blender functions (for truecolor modes). Because it
73       involves  reading  as  well  as  writing the bitmap memory, translucent
74       drawing is very slow if you draw directly to  video  RAM,  so  wherever
75       possible you should use a memory bitmap instead.
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SEE ALSO

79       xor_mode(3),  solid_mode(3),  color_map(3), set_trans_blender(3), exal‐
80       pha(3), excolmap(3), exjoy(3), expat(3), extrans(3)
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84Allegro                          version 4.4.3                 drawing_mode(3)
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