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Acorn Arcade forums: Programming: Rotated & scaled sprite plotting
 
  Rotated & scaled sprite plotting
  MrTAToad (01:35 11/2/2013)
 
Nicholas Kingsley Message #121893, posted by MrTAToad at 01:35, 11/2/2013
Member
Posts: 36 		I've got SpriteOp 56 displaying rotated and scaled sprites now.

However, the origin of the plotting is at the bottom left, whilst I want it to be the middle (ie subtract half the width and height off the X & Y position of the sprite).

My translation code is currently (with sinp and cosp being the radian of an angle) :

scaleMatrix[0]=(int) ((endScale*cosp)*65536.0);
scaleMatrix[1]=(int) ((endScale*sinp)*65536.0);
scaleMatrix[2]=(int) ((endScale*-sinp)*65536.0);
scaleMatrix[3]=(int) ((endScale*cosp)*65536.0);
scaleMatrix[4]=nx*256;
scaleMatrix[5]=ny*256;

sourceCoords[0]=animXPos;
sourceCoords[1]=animXPos;
sourceCoords[2]=useWidth;
sourceCoords[3]=useHeight;

inreg.r[0]=56+512;
inreg.r[1]=(int) spriteInfo->spriteBlockInfo->spriteArea;
inreg.r[2]=(int) spriteInfo->spritePtr;
inreg.r[3]=1<<1;
inreg.r[4]=(int) &sourceCoords;
inreg.r[5]=0+8;
inreg.r[6]=(int) &scaleMatrix;
inreg.r[7]=-1;
_kernel_swi(OS_SpriteOp,&inreg,&outreg);

Would the scaling matrix need to take into account half the width/height of the sprite or are the coordinate values incorrect ? I presume to convert from Draw units to OS units would be multiplication by 256...

nx and ny have been converted to OS units beforehand

[Edited by MrTAToad at 01:36, 11/2/2013]
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Acorn Arcade forums: Programming: Rotated & scaled sprite plotting