With a 6 Mhz z80 and 128k ram, it's possible to program just about anything. But the qeustion is whether or not you want do it. Bitmap rotation has always been hot topic in graphics programming. Matt Johnson (cool guy who created 86 Central) and I were talking about this a while ago, and I have attached the html document that he found on it. If you look at the last part of the C source, you'll see a pretty simple, yet intensive loop for drawing a rotated bitmap (sprite). The first thing you'll notice is that there is trig and multiplications being done in the loop. You'd have to store preculated trig tables for both sine and cosine (you'd end up storing the first quadrant and creating the rest at runtime...good example is Matthew Shepcar's Peaworm), which would take up a good amount of space. The next thing you'll notice is that they're doing a lot of floating point calculations in the inner loop. That's almost always a no in any time-critical graphics function (unless you have a math coprocessor and the float and integer operations are interleaved in the loop, in which case you save time because the integer cpu doesn't have to waste time with fixed point calculations). You would have to use fixed point numbers, which will be a little tricky on an 8-bit processor. There are also two multiplies for each pixel on the inner loop, and two per line in the outer loop. Not fun with fixed point. Now, it could be done, though it would be very slow for a sprite routine. And the problem would be that using small sprites (8x8 or even 16x16) would introduce so many errors that the rotated sprites would look horrible (I wrote a fairly large space shooter in c++ using a simple routine like the one here, and the sprites look pretty bad). Pre-rotating a few sprites doesn't sound so bad now, does it? :) > > is there any way to display a sprite then rotate it without having to draw all > the sprites in the prog > a routine could take the x,y cords a pointer to the sprite and a angle of > rotation > is this possible at all???????Title: DN - Re: 2D Bitmap rotation.
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Steven wrote:
>
> Does anyone know if there any free source code in 'C' for rotating a
> bitmap? Very Urgently, any help would be appreciated.
The trick is to think backwards. Instead or rotating the source bitmap,
scan the destination bitmap and find where the corresponding bit(s)
would
be in a rotated version of the source bitmap. Here is some C code for
rotating a PGM image -- should be cake to make it work with bitmaps.
good luck
--wayne
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "pixel.h"
#include "pgm.h"
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define D2R(D) ((D)*(M_PI/180.0))
#define BACKGROUND 0
int main(int argc, char *argv[]) {
PIXEL *image, *dstimage;
PGM_ERROR error;
int width, height;
double w2, h2;
int i,j;
double angle, sine, cosine;
if (argc != 4) {
printf("syntax: %s <degrees> <input pgm file name> <out pgm file
name>\n",
argv[0]);
exit (-1);
}
angle = D2R(atof(argv[1]));
if ((image = pgmGetImage(argv[2], &width, &height, &error)) == NULL) {
fprintf(stderr, "error reading image `%s'!\n", argv[2]);
exit(-1);
}
if ((dstimage = (PIXEL *) malloc(width*height*sizeof(PIXEL))) == NULL)
{
perror("malloc");
exit(-1);
}
sine = sin(angle);
cosine = cos(angle);
w2 = width/2.0;
h2 = height/2.0;
for (i = 0; i < height; i++) {
double x, y = i - h2;
double ysine = y*sine, ycosine = y*cosine;
for (j = 0; j < width; j++) {
double srcx, srcy;
int srci, srcj;
x = j - w2;
srcx = x*cosine + ysine;
srcy = -x*sine + ycosine;
srci = (int) (srcy + h2 + 0.5);
srcj = (int) (srcx + w2 + 0.5);
if (srci < 0 || srci >= height || srcj < 0 || srcj >= width)
PUTPIXEL(dstimage,j,i,width,BACKGROUND);
else {
int pixel = GETPIXEL(image,srcj,srci,width);
PUTPIXEL(dstimage,j,i,width,pixel);
}
}
}
if ((error = pgmPutImage (argv[3], dstimage, width, height))
!= PGM_NO_ERROR) {
fprintf(stderr, "error writing image `%s'!\n", argv[3]);
exit(-1);
}
return 0;
}
--
Wayne O. Cochran
wcochran@eecs.wsu.edu
http://www.eecs.wsu.edu/~wcochran
Ecclesiastes 3:11
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