drawing_mode - Man Page

#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
                                   drawing
   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.

DRAW_MODE_MASKED_PATTERN is almost the same as DRAW_MODE_SOLID_PATTERN,  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(3), solid_mode(3), color_map(3), set_trans_blender(3), exalpha(3), excolmap(3), exjoy(3), expat(3), extrans(3)

arc(3), circle(3), circlefill(3), color_map(3), ellipse(3), ellipsefill(3), exalpha(3), excolmap(3), exjoy(3), expat(3), extrans(3), fastline(3), floodfill(3), hline(3), line(3), polygon(3), POLYTYPE_FLAT(3), putpixel(3), rect(3), rectfill(3), set_add_blender(3), set_blender_mode(3), set_burn_blender(3), set_color_blender(3), set_difference_blender(3), set_dissolve_blender(3), set_dodge_blender(3), set_hue_blender(3), set_invert_blender(3), set_luminance_blender(3), set_multiply_blender(3), set_saturation_blender(3), set_screen_blender(3), set_trans_blender(3), set_write_alpha_blender(3), solid_mode(3), spline(3), triangle(3), vline(3), xor_mode(3).