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:   Concepts: graphics^zooming
 17:   Concepts: drawing^zooming
 18:   Concepts: zooming^in graphics

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

 30:   PetscDrawIsNull(draw,&isnull);
 31:   if (isnull) return(0);

 33:   PetscDrawCheckResizedWindow(draw);
 34:   PetscDrawClear(draw);
 35:   PetscDrawCollectiveBegin(draw);
 36:   (*func)(draw,ctx);
 37:   PetscDrawCollectiveEnd(draw);
 38:   PetscDrawFlush(draw);

 40:   PetscDrawGetPause(draw,&dpause);
 41:   if (dpause >= 0) {
 42:     PetscSleep(dpause);
 43:     goto theend;
 44:   }
 45:   if (dpause != -1) goto theend;

 47:   PetscDrawGetMouseButton(draw,&button,&xc,&yc,NULL,NULL);
 48:   PetscDrawGetCoordinates(draw,&xl,&yl,&xr,&yr);
 49:   xmin = xl; xmax = xr; w = xr - xl;
 50:   ymin = yl; ymax = yr; h = yr - yl;

 52:   while (button != PETSC_BUTTON_NONE && button != PETSC_BUTTON_RIGHT) {
 53:     switch (button) {
 54:     case PETSC_BUTTON_LEFT:       scale = 0.5;   break;
 55:     case PETSC_BUTTON_CENTER:     scale = 2.0;   break;
 56:     case PETSC_BUTTON_WHEEL_UP:   scale = 8/10.; break;
 57:     case PETSC_BUTTON_WHEEL_DOWN: scale = 10/8.; break;
 58:     default:                      scale = 1.0;
 59:     }
 60:     xl = scale*(xl + w - xc) + xc - w*scale;
 61:     xr = scale*(xr - w - xc) + xc + w*scale;
 62:     yl = scale*(yl + h - yc) + yc - h*scale;
 63:     yr = scale*(yr - h - yc) + yc + h*scale;
 64:     w *= scale; h *= scale;
 65:     PetscDrawClear(draw);
 66:     PetscDrawSetCoordinates(draw,xl,yl,xr,yr);
 67:     PetscDrawCollectiveBegin(draw);
 68:     (*func)(draw,ctx);
 69:     PetscDrawCollectiveEnd(draw);
 70:     PetscDrawFlush(draw);
 71:     PetscDrawGetMouseButton(draw,&button,&xc,&yc,NULL,NULL);
 72:   }
 73:   PetscDrawSetCoordinates(draw,xmin,ymin,xmax,ymax);
 74: theend:
 75:   return(0);
 76: }