[hypnotoad] writes: While pure-script image scaling is "nice" for one-off projects, many of us need something that is fast, and capable of scaling images into arbitrary scale factors. Below is a routine that is based in C that we use in production to scale ship templates to fit on a canvas for tracing. As users need different levels of detail, it had to scale and line up pixel-for pixel for what was being overlaid on the canvas.

======

/*
** Scale an image using grid sampling
** Please note this implementation will crash if the
** destination image was not already created 
**
** Arguments: srcimg newwidth newheight destimg alpha
** srcimg: A photo object created with "image create photo"
** newwidth: The new width of the image in pixels
** newheight: The new height of the image in pixels
** destimage: Name for the resulting image
** alpha: Alpha to apply to the image (1 - opaque, 0-clear)
*/
static int irmScaleImgCmd(
  void *pArg,
  Tcl_Interp *interp,
  int objc,
  Tcl_Obj *CONST objv[]
){
    char *srcName, *destName;
    Tk_PhotoImageBlock srcBlock,destBlock;
    Tk_PhotoHandle srcImage,destImage;
    int di,dj;
    double scalex,scaley,sx2,sy2,newalpha;
    int returnCode;
    
    int width,height,newwid,newhgt;
    if( objc != 5 && objc !=6){
        Tcl_WrongNumArgs(interp, 1, objv, "srcimg newwid newhgt destimg ?alpha?");
        return TCL_ERROR;
    }
    srcName=Tcl_GetString(objv[1]);
    if(Tcl_GetIntFromObj(interp,objv[2],&newwid)) return TCL_ERROR;
    if(Tcl_GetIntFromObj(interp,objv[3],&newhgt)) return TCL_ERROR;
    destName=Tcl_GetString(objv[4]);
    if(objc==6) {
        if(Tcl_GetDoubleFromObj(interp,objv[5],&newalpha)) return TCL_ERROR;
    } else {
        newalpha=1.0;
    }
    if(newalpha>1.0) {
        newalpha=1.0;
    }

    srcImage=Tk_FindPhoto(interp, srcName);
    Tk_PhotoGetSize(srcImage,&width,&height);
    Tk_PhotoGetImage(srcImage,&srcBlock);
    if(srcBlock.pixelSize != 4 && srcBlock.pixelSize!=3) {
        Tcl_AppendResult(interp, "I can't make heads or tails from this image, the bitfield is neither 3 nor 4",(char*)0);
        return TCL_ERROR;
    }

    destImage=Tk_FindPhoto(interp, destName);
    Tk_PhotoBlank(destImage);
    Tk_PhotoSetSize(interp,destImage,newwid,newhgt);    

    destBlock.width=newwid;
    destBlock.height=newhgt;
    
    scalex=(double)srcBlock.width/(double)newwid;
    scaley=(double)srcBlock.height/(double)newhgt;
    sx2=scalex/2.0;
    sy2=scaley/2.0;

    destBlock.pixelSize=4;
    destBlock.pitch=newwid * 4;
    destBlock.offset[0] = 0; 
    destBlock.offset[1] = 1; 
    destBlock.offset[2] = 2; 
    destBlock.offset[3] = 3;
    destBlock.pixelPtr=(unsigned char *)Tcl_Alloc(destBlock.width*destBlock.height*4);

    

    /* Loop through and scale */
    for(dj=0;dj<destBlock.height;dj++) {
        for(di=0;di<destBlock.width;di++) {
            int si,sj;
            int cx=(int)(di*scalex);
            int cy=(int)(dj*scaley);
            int points=1;
            double red=0.0,green=0.0,blue=0.0,alpha=0.0;
            int newoff=destBlock.pitch*dj+destBlock.pixelSize*di;
            int startoff=srcBlock.pitch*cy+srcBlock.pixelSize*cx;

            red=(double)srcBlock.pixelPtr[startoff+srcBlock.offset[0]];
            green=(double)srcBlock.pixelPtr[startoff+srcBlock.offset[1]];
            blue=(double)srcBlock.pixelPtr[startoff+srcBlock.offset[2]];
            if(srcBlock.pixelSize==4) {
                alpha=(double)srcBlock.pixelPtr[startoff+srcBlock.offset[3]];
            } else {
                alpha=alpha+255;
            }
            for(sj=(int)cy-sy2;sj<(int)cy+sy2;sj++) {
                if(sj < 0) continue;
                if(sj > srcBlock.height) continue;
                for(si=(int)cx-sx2;si<(int)cx+sx2;si++) {
                    if(si < 0) continue;
                    if(si > srcBlock.width) continue;
                    int offset=srcBlock.pitch*sj+srcBlock.pixelSize*si;
                    points++;
                    red=red+ (double)srcBlock.pixelPtr[offset+srcBlock.offset[0]];
                    green=green+ (double)srcBlock.pixelPtr[offset+srcBlock.offset[1]];
                    blue=blue+ (double)srcBlock.pixelPtr[offset+srcBlock.offset[2]];
                    if(srcBlock.pixelSize==4) {
                        alpha=alpha+ (double)srcBlock.pixelPtr[offset+srcBlock.offset[3]];
                    } else {
                        alpha=alpha+255;
                    }
                }
            }
            destBlock.pixelPtr[newoff+destBlock.offset[0]]=(unsigned char)(red/points);
            destBlock.pixelPtr[newoff+destBlock.offset[1]]=(unsigned char)(green/points);
            destBlock.pixelPtr[newoff+destBlock.offset[2]]=(unsigned char)(blue/points);
            destBlock.pixelPtr[newoff+destBlock.offset[3]]=(unsigned char)(alpha*newalpha/points);
        }
    }
    returnCode=Tk_PhotoPutBlock(interp,destImage,&destBlock,0,0,destBlock.width,destBlock.height,TK_PHOTO_COMPOSITE_SET);
    return returnCode;
}


/*
** The following is the only public symbol in this source file.  .
*/
int DLLEXPORT Imgscale_Init(Tcl_Interp *interp){
    Tcl_CreateObjCommand(interp, "image_scale", irmScaleImgCmd, 0, 0);
    return TCL_OK;
}
======


----
'''[RZ] - 2010-02-04 10:34:03'''

Any chance of including this in the tk [[[image]]] command?

----
[ralfixx] Note: it seems TK 8.5 is required for this. I get SEGVs with 8.3.3

<<categories>> Category Image Processing | Arts and crafts of Tcl-Tk programming