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Blitting and sprites



All these routines are affected by the clipping rectangle of the destination bitmap.

void clear_bitmap(BITMAP *bitmap);
Clears the bitmap to color 0.

void clear(BITMAP *bitmap);
An alias for clear_bitmap(), provided for backwards compatibility. It is implemented as a static inline function. The aliasing may be switched off by defining the preprocessor symbol ALLEGRO_NO_CLEAR_BITMAP_ALIAS before including Allegro headers, eg: 

      #define ALLEGRO_NO_CLEAR_BITMAP_ALIAS
      #include <allegro.h>
void clear_to_color(BITMAP *bitmap, int color);
Clears the bitmap to the specified color.

void blit(BITMAP *source, BITMAP *dest, int source_x, int source_y, int dest_x, int dest_y, int width, int height);
Copies a rectangular area of the source bitmap to the destination bitmap. The source_x and source_y parameters are the top left corner of the area to copy from the source bitmap, and dest_x and dest_y are the corresponding position in the destination bitmap. This routine respects the destination clipping rectangle, and it will also clip if you try to blit from areas outside the source bitmap.

You can blit between any parts of any two bitmaps, even if the two memory areas overlap (ie. source and dest are the same, or one is sub-bitmap of the other). You should be aware, however, that a lot of SVGA cards don't provide separate read and write banks, which means that blitting from one part of the screen to another requires the use of a temporary bitmap in memory, and is therefore extremely slow. As a general rule you should avoid blitting from the screen onto itself in SVGA modes.

In mode-X, on the other hand, blitting from one part of the screen to another can be significantly faster than blitting from memory onto the screen, as long as the source and destination are correctly aligned with each other. Copying between overlapping screen rectangles is slow, but if the areas don't overlap, and if they have the same plane alignment (ie. (source_x%4) == (dest_x%4)), the VGA latch registers can be used for a very fast data transfer. To take advantage of this, in mode-X it is often worth storing tile graphics in a hidden area of video memory (using a large virtual screen), and blitting them from there onto the visible part of the screen.

If the GFX_HW_VRAM_BLIT bit in the gfx_capabilities flag is set, the current driver supports hardware accelerated blits from one part of the screen onto another. This is extremely fast, so when this flag is set it may be worth storing some of your more frequently used graphics in an offscreen portion of the video memory.

Unlike most of the graphics routines, blit() allows the source and destination bitmaps to be of different color depths, so it can be used to convert images from one pixel format to another.

void masked_blit(BITMAP *source, BITMAP *dest, int source_x, int source_y, int dest_x, int dest_y, int width, int height);
Like blit(), but skips transparent pixels, which are marked by a zero in 256 color modes or bright pink for truecolor data (maximum red and blue, zero green). The source and destination regions must not overlap.

If the GFX_HW_VRAM_BLIT_MASKED bit in the gfx_capabilities flag is set, the current driver supports hardware accelerated masked blits from one part of the screen onto another. This is extremely fast, so when this flag is set it may be worth storing some of your more frequently used sprites in an offscreen portion of the video memory.

Warning: if the hardware acceleration flag is not set, masked_blit() will not work correctly when used with a video memory source image, and the input graphic must always be a memory bitmap!

void stretch_blit(BITMAP *source, BITMAP *dest, int source_x, source_y, source_width, source_height, int dest_x, dest_y, dest_width, dest_height);
Like blit(), except it can scale images so the source and destination rectangles don't need to be the same size. This routine doesn't do as much safety checking as the regular blit: in particular you must take care not to copy from areas outside the source bitmap, and you cannot blit between overlapping regions, ie. you must use different bitmaps for the source and the destination. Also, the source must be a memory bitmap or sub-bitmap, not the hardware screen.

void masked_stretch_blit(BITMAP *source, BITMAP *dest, int source_x, source_y, source_w, source_h, int dest_x, dest_y, dest_w, dest_h);
Like stretch_blit(), but skips transparent pixels, which are marked by a zero in 256 color modes or bright pink for truecolor data (maximum red and blue, zero green). The source and destination regions must not overlap.

void draw_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y);
Draws a copy of the sprite bitmap onto the destination bitmap at the specified position. This is almost the same as blit(sprite, bmp, 0, 0, x, y, sprite->w, sprite->h), but it uses a masked drawing mode where transparent pixels are skipped, so the background image will show through the masked parts of the sprite. Transparent pixels are marked by a zero in 256 color modes or bright pink for truecolor data (maximum red and blue, zero green).

If the GFX_HW_VRAM_BLIT_MASKED bit in the gfx_capabilities flag is set, the current driver supports hardware accelerated sprite drawing when the source image is a video memory bitmap or a sub-bitmap of the screen. This is extremely fast, so when this flag is set it may be worth storing some of your more frequently used sprites in an offscreen portion of the video memory.

Warning: if the hardware acceleration flag is not set, draw_sprite() will not work correctly when used with a video memory source image, and the input graphic must always be a memory bitmap!

Although generally not supporting graphics of mixed color depths, as a special case this function can be used to draw 256 color source images onto truecolor destination bitmaps, so you can use palette effects on specific sprites within a truecolor program.

void draw_sprite_v_flip(BITMAP *bmp, BITMAP *sprite, int x, int y);
void draw_sprite_h_flip(BITMAP *bmp, BITMAP *sprite, int x, int y);
void draw_sprite_vh_flip(BITMAP *bmp, BITMAP *sprite, int x, int y);
These are like draw_sprite(), but they flip the image about the vertical, horizontal, or both, axes. This produces exact mirror images, which is not the same as rotating the sprite (and it is a lot faster than the rotation routine). The sprite must be a memory bitmap.

void draw_trans_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y);
Uses the global color_map table or truecolor blender functions to overlay the sprite 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. The bitmap and sprite must normally be in the same color depth, but as a special case you can draw 32 bit RGBA format sprites onto any hicolor or truecolor bitmap, as long as you call set_alpha_blender() first, and you can draw 8 bit alpha images onto a 32 bit RGBA destination, as long as you call set_write_alpha_blender() first.

void draw_lit_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int color);
Tints the sprite image to the specified color or light level, using the global color_map table, and draws the resulting image to the destination bitmap. This must only be used after you have set up the color mapping table (for 256 color modes) or blender functions (for truecolor modes).

void draw_gouraud_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int c1, int c2, int c3, int c4);
Tints the sprite to the specified color or light level, interpolating the four corner colors across the surface of the 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).

void draw_character(BITMAP *bmp, BITMAP *sprite, int x, int y, int color);
Draws a copy of the sprite bitmap onto the destination bitmap at the specified position, drawing transparent pixels in the current text mode (skipping them if the text mode is -1, otherwise drawing them in the text background color), and setting all other pixels to the specified color. Transparent pixels are marked by a zero in 256 color modes or bright pink for truecolor data (maximum red and blue, zero green). The sprite must be an 8 bit image, even if the destination is a truecolor bitmap.

void rotate_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, fixed angle);
Draws the sprite image onto the bitmap. It is placed with its top left corner at the specified position, then rotated by the specified angle around its centre. The angle is a fixed point 16.16 number in the same format used by the fixed point trig routines, with 256 equal to a full circle, 64 a right angle, etc. All rotation functions can draw between any two bitmaps, even screen bitmaps or bitmaps of different color depth.

void rotate_sprite_v_flip(BITMAP *bmp, BITMAP *sprite, int x, int y, fixed angle);
Like rotate_sprite, but also flips the image vertically. To flip horizontally, use this routine but add itofix(128) to the angle. To flip in both directions, use rotate_sprite() and add itofix(128) to its angle.

void rotate_scaled_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, fixed angle, fixed scale);
Like rotate_sprite(), but stretches or shrinks the image at the same time as rotating it.

void rotate_scaled_sprite_v_flip(BITMAP *bmp, BITMAP *sprite, int x, int y, fixed angle, fixed scale)
Draws the sprite, similar to rotate_scaled_sprite() except that it flips the sprite vertically first.

void pivot_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int cx, int cy, fixed angle);
Like rotate_sprite(), but aligns the point in the sprite given by (cx, cy) to (x, y) in the bitmap, then rotates around this point.

void pivot_sprite_v_flip(BITMAP *bmp, BITMAP *sprite, int x, int y, int cx, int cy, fixed angle);
Like rotate_sprite_v_flip(), but aligns the point in the sprite given by (cx, cy) to (x, y) in the bitmap, then rotates around this point.

void pivot_scaled_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int cx, int cy, fixed angle, fixed scale));
Like rotate_scaled_sprite(), but aligns the point in the sprite given by (cx, cy) to (x, y) in the bitmap, then rotates and scales around this point.

void pivot_scaled_sprite_v_flip(BITMAP *bmp, BITMAP *sprite, int x, int y, fixed angle, fixed scale)
Like rotate_scaled_sprite_v_flip(), but aligns the point in the sprite given by (cx, cy) to (x, y) in the bitmap, then rotates and scales around this point.

void stretch_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int w, int h);
Draws the sprite image onto the bitmap at the specified position, stretching it to the specified width and height. The difference between stretch_sprite() and stretch_blit() is that stretch_sprite() masks out transparent pixels, which are marked by a zero in 256 color modes or bright pink for truecolor data (maximum red and blue, zero green).