2:  #include <petscdraw.h>

  4: /*@C
  5:     PetscDrawZoom - Allows one to create a graphic that users may zoom into.

  7:     Collective on PetscDraw

  9:     Input Parameters:
 10: +   draw - the window where the graph will be made.
 11: .   func - users function that draws the graphic
 12: -   ctx - pointer to any user required data

 14:   Level: advanced

 16: .seealso:
 17: @*/
 18: PetscErrorCode  PetscDrawZoom(PetscDraw draw,PetscErrorCode (*func)(PetscDraw,void*),void *ctx)
 19: {
 20:   PetscErrorCode  ierr;
 21:   PetscDrawButton button;
 22:   PetscReal       dpause,xc,yc,scale = 1.0,w,h,xr,xl,yr,yl,xmin,xmax,ymin,ymax;
 23:   PetscBool       isnull;

 26:   PetscDrawIsNull(draw,&isnull);
 27:   if (isnull) return(0);

 29:   PetscDrawCheckResizedWindow(draw);
 30:   PetscDrawClear(draw);
 31:   PetscDrawCollectiveBegin(draw);
 32:   (*func)(draw,ctx);
 33:   PetscDrawCollectiveEnd(draw);
 34:   PetscDrawFlush(draw);

 36:   PetscDrawGetPause(draw,&dpause);
 37:   if (dpause >= 0) {
 38:     PetscSleep(dpause);
 39:     goto theend;
 40:   }
 41:   if (dpause != -1) goto theend;

 43:   PetscDrawGetMouseButton(draw,&button,&xc,&yc,NULL,NULL);
 44:   PetscDrawGetCoordinates(draw,&xl,&yl,&xr,&yr);
 45:   xmin = xl; xmax = xr; w = xr - xl;
 46:   ymin = yl; ymax = yr; h = yr - yl;

 48:   while (button != PETSC_BUTTON_NONE && button != PETSC_BUTTON_RIGHT) {
 49:     switch (button) {
 50:     case PETSC_BUTTON_LEFT:       scale = 0.5;   break;
 51:     case PETSC_BUTTON_CENTER:     scale = 2.0;   break;
 52:     case PETSC_BUTTON_WHEEL_UP:   scale = 8/10.; break;
 53:     case PETSC_BUTTON_WHEEL_DOWN: scale = 10/8.; break;
 54:     default:                      scale = 1.0;
 55:     }
 56:     xl = scale*(xl + w - xc) + xc - w*scale;
 57:     xr = scale*(xr - w - xc) + xc + w*scale;
 58:     yl = scale*(yl + h - yc) + yc - h*scale;
 59:     yr = scale*(yr - h - yc) + yc + h*scale;
 60:     w *= scale; h *= scale;
 61:     PetscDrawClear(draw);
 62:     PetscDrawSetCoordinates(draw,xl,yl,xr,yr);
 63:     PetscDrawCollectiveBegin(draw);
 64:     (*func)(draw,ctx);
 65:     PetscDrawCollectiveEnd(draw);
 66:     PetscDrawFlush(draw);
 67:     PetscDrawGetMouseButton(draw,&button,&xc,&yc,NULL,NULL);
 68:   }
 69:   PetscDrawSetCoordinates(draw,xmin,ymin,xmax,ymax);
 70: theend:
 71:   return(0);
 72: }