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Bitmaps
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Define a tructure to store the bitmap data
in. Essentially its just an array of bytes for the pixel data:
typedef struct bitMap_type
{
unsigned char *pixels;
unsigned int width,height;
}bitmap;
This structure can now be drawn to the screen with this code:
void bit_blt(int x, int y,bitmap *bm)
{
int xindex, yindex,bml=0, offset = (y << 8) + (y << 6)
+ x;
for (yindex = 0; yindex < bm->height; yindex++)
{
for (xindex = 0; xindex < bm->width; xindex++)
double_buffer[offset+xindex] = bm->pixels[xindex+bml];
offset += 320; // next line buffer
bml += bm->width; // next line bitmap
}
}
Note that this code assumes 320 X 200 resolution.
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loading
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To create good sprites you will want to import them
from a paint program. Here is the code to load a 256 colour bitmap
into the structure given above.
void loadBitmap(bitmap *bmPtr,char *fileName,char
freeFlag)
{
unsigned int i,j;
FILE *bmpFile= fopen(fileName,"rb");
if(freeFlag)
free(bmPtr->pixels);
fseek(bmpFile,18,SEEK_SET);
fread(&bmPtr->width,4,1,bmpFile);
fread(&bmPtr->height,4,1,bmpFile);
bmPtr->pixels=(char*)malloc(bmPtr->height*bmPtr->width);
fseek(bmpFile,1078,SEEK_SET);
for(i=0;i<bmPtr->height;i++)
for(j=0;j<bmPtr->width;j++)
bmPtr->pixels[(bmPtr->height-1-i)*bmPtr->width+j]=fgetc(bmpFile);
fclose(bmpFile);
}
Note: This code does not account for pixel data in the bitmap file
being zero-padded to end on 32-bit boundaries. Subsequently it will
only correctly load bitmaps with a width divisible by four.
Download
a working example
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Transparancy
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Transparant sections can be included in sprites quite easily. Just
use a particular pallette index as the transparant colour. Zero
is a sensible choice. Now ammend the drawing code:
void trans_bit_blt(int x, int y,bitmap *bm)
{
int xindex, yindex,bml=0, offset = (y << 8) + (y <<
6) + x;
for (yindex = 0; yindex < bm->height; yindex++)
{
for (xindex = 0; xindex < bm->width; xindex++)
if (bm->pixels[xindex+bml])
.................................................................
And thats it! Download
a working example
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Clipping
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If you try to draw a sprite and it is even partly offscreen, the
computer will crash. This drawing function will prevent this occuring
along the X axis, and will draw partially on-screen images.
void clipped_trans_bit_blt(int x, int y,bitmap
*bm)
{
int xindex, yindex,bml=0,offset=(y<<8) + (y<<6) +x;
y=0;
if(x<0)
{
y=abs(x);
x=bm->width-abs(x);
}
else if(x+bm->width>319)
{
x=319-x;
}
else
{
x=bm->width;
}
for (yindex = 0; yindex < bm->height; yindex++)
{
for (xindex = y; xindex < y+x; xindex++)
if (bm->pixels[xindex+bml])
double_buffer[offset+xindex] = bm->pixels[xindex+bml];
offset += 320;
bml += bm->width;
}
}
You should now be able to move sprites around the screen (just be
carefull on the Y axis!). Download
a working example
If your confident with this the next step is to get animation underway,
but I'll leave that to you...
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