rotozumer is a routine that displays bitmap
on screen (which is also a bitmap so this is like
copying bitmap onto bitmap) but the input bitmap
(you may call it 'sprite') will be rotated by given angle and scaled by given zoom

the method is just to iterate on spirite all pixels, totate them (this is multiply by
rotated base vectors that
sescribes rotation and zoom) and set this roteted zoomed pixels to screen (yet if
zoom is like 2.0 the sampling of the input should be not by +1 step but more like
+0.5 to not make holes in output)

my unoptymised and not much edited for names etc function for this is that

inline void Rotate2d(float* x, float* y, float angle)
{
float xt = (*x) * cos(angle*degree360) - (*y) * sin(angle*degree360);
float yt = (*x) * sin(angle*degree360) + (*y) * cos(angle*degree360);

*x = xt;
*y = yt;
}


void DrawSprite2(float pos_x,
float pos_y,
char* file,
int sprite_bitmap_pos_x,
int sprite_bitmap_pos_y,
int sprite_bitmap_end_x,
int sprite_bitmap_end_y,
float angle = 0 ,
float zoom = 1,
int sprite_centre_bitmap_x = -1,
int sprite_centre_bitmap_y = -1

)

{

if(sprite_centre_bitmap_x<0 || sprite_centre_bitmap_y<0)
{
sprite_centre_bitmap_x = (sprite_bitmap_pos_x + sprite_bitmap_end_x)/2;
sprite_centre_bitmap_y = (sprite_bitmap_pos_y + sprite_bitmap_end_y)/2;

}


float sprite_width = sprite_bitmap_end_x - sprite_bitmap_pos_x + 1 ;
float sprite_height = sprite_bitmap_end_y - sprite_bitmap_pos_y + 1;



float Ax = sprite_bitmap_pos_x - sprite_centre_bitmap_x ;
float Ay = sprite_bitmap_pos_y - sprite_centre_bitmap_y ;
float Bx = sprite_bitmap_end_x - sprite_centre_bitmap_x ;
float By = sprite_bitmap_pos_y - sprite_centre_bitmap_y ;
float Cx = sprite_bitmap_end_x - sprite_centre_bitmap_x ;
float Cy = sprite_bitmap_end_y - sprite_centre_bitmap_y ;
float Dx = sprite_bitmap_pos_x - sprite_centre_bitmap_x ;
float Dy = sprite_bitmap_end_y - sprite_centre_bitmap_y ;

Rotate2d(&Ax,&Ay, angle);
Rotate2d(&Bx,&By, angle);
// Rotate2d(&Cx,&Cy, angle);
Rotate2d(&Dx,&Dy, angle);


float dxdx = (Bx-Ax)/sprite_width;
float dydx = (By-Ay)/sprite_width;

float dxdy = (Dx-Ax)/sprite_height;
float dydy = (Dy-Ay)/sprite_height;

float x, y;


for(float j=sprite_bitmap_pos_y-sprite_centre_bitmap_y;
j<sprite_bitmap_end_y-sprite_centre_bitmap_y; j+=.7/zoom)
{
for(float i=sprite_bitmap_pos_x-sprite_centre_bitmap_x;
i<sprite_bitmap_end_x-sprite_centre_bitmap_x; i+=.7/zoom)
{
unsigned color = sprites_buf_[sprite_centre_bitmap_y +
int(j)][sprite_centre_bitmap_x + int(i)];

x = 0*sprite_centre_bitmap_x + i * dxdx*zoom + j*dxdy*zoom;
y = 0*sprite_centre_bitmap_y + i * dydx*zoom + j*dydy*zoom;

if(color==0) {} else SetPixelSafe(pos_x + x, pos_y + y, color);


}
}


}


the problem is clipping, if sprite is rotated positioned and zoomed often quite large
parts and a lot of pixels destinate out the screen - and here in that routine i clib
them all per pixel (in "SetPixelSafe")

this is much wastefull, and optimistation of this routine is very important as
sprites, esp big sprites or sprites that are zoomed to be big may take real lot of
time on cpu
(rotozuming big screen size or overscreen sprites sadly may take like 40 ms which is
deadly slow (where small ones may take like 1 ms which is ok)

so how to speed it up?
(id someone want to see how it runs i may ulpoad te win32 exe showing how it worx)