drawing_mode(3alleg4)            Allegro manual            drawing_mode(3alleg4)

       drawing_mode - Sets the graphics drawing mode. Allegro game programming

       #include <allegro.h>

       void drawing_mode(int mode, BITMAP *pattern, int x_anchor, int y_anchor);

       Sets the graphics drawing mode. This only affects the geometric routines
       like putpixel, lines, rectangles, circles, polygons, floodfill, etc, not
       the text output, blitting, or sprite drawing functions. The mode should
       be one of the following constants:

          DRAW_MODE_SOLID               - the default, solid color
          DRAW_MODE_XOR                 - exclusive-or drawing
          DRAW_MODE_COPY_PATTERN        - multicolored pattern fill
          DRAW_MODE_SOLID_PATTERN       - single color pattern fill
          DRAW_MODE_MASKED_PATTERN      - masked pattern fill
          DRAW_MODE_TRANS               - translucent color blending

       In DRAW_MODE_SOLID, pixels of the bitmap being drawn onto are simply
       replaced by those produced by the drawing function.

       In DRAW_MODE_XOR, pixels are written to the bitmap with an exclusive-or
       operation rather than a simple copy, so drawing the same shape twice will
       erase it. Because it involves reading as well as writing the bitmap
       memory, xor drawing is a lot slower than the normal replace mode.

       With the patterned modes, you provide a pattern bitmap which is tiled
       across the surface of the shape. Allegro stores a pointer to this bitmap
       rather than copying it, so you must not destroy the bitmap while it is
       still selected as the pattern. The width and height of the pattern must
       be powers of two, but they can be different, eg. a 64x16 pattern is fine,
       but a 17x3 one is not. The pattern is tiled in a grid starting at point
       (x_anchor, y_anchor). Normally you should just pass zero for these
       values, which lets you draw several adjacent shapes and have the patterns
       meet up exactly along the shared edges. Zero alignment may look peculiar
       if you are moving a patterned shape around the screen, however, because
       the shape will move but the pattern alignment will not, so in some
       situations you may wish to alter the anchor position.

       When you select DRAW_MODE_COPY_PATTERN, pixels are simply copied from the
       pattern bitmap onto the destination bitmap. This allows the use of
       multicolored patterns, and means that the color you pass to the drawing
       routine is ignored. This is the fastest of the patterned modes.

       In DRAW_MODE_SOLID_PATTERN, each pixel in the pattern bitmap is compared
       with the mask color, which is zero in 256-color modes or bright pink for
       truecolor data (maximum red and blue, zero green). If the pattern pixel
       is solid, a pixel of the color you passed to the drawing routine is
       written to the destination bitmap, otherwise a zero is written. The
       pattern is thus treated as a monochrome bitmask, which lets you use the
       same pattern to draw different shapes in different colors, but prevents
       the use of multicolored patterns.

       but the masked pixels are skipped rather than being written as zeros, so
       the background shows through the gaps.

       In DRAW_MODE_TRANS, the global color_map table or truecolor blender
       functions are used to overlay pixels on top of the existing image. This
       must only be used after you have set up the color mapping table (for 256
       color modes) or blender functions (for truecolor modes). Because it
       involves reading as well as writing the bitmap memory, translucent
       drawing is very slow if you draw directly to video RAM, so wherever
       possible you should use a memory bitmap instead.

       xor_mode(3alleg4), solid_mode(3alleg4), color_map(3alleg4),
       set_trans_blender(3alleg4), exalpha(3alleg4), excolmap(3alleg4),
       exjoy(3alleg4), expat(3alleg4), extrans(3alleg4)

Allegro                           version 4.4.3            drawing_mode(3alleg4)