Getting Started > For Beginners > Zooming In on a Selection > Zooming In on a Selection: Step 3

Zooming In on a Selection: Step 3

/* Save the starting position in screen pixels (used by GDI functions) */   
StartGDIX = point.x;   
StartGDIY = point.y;   
/* Use the mouse position's percentage offsets in the image rectangle   
to determine the pixel offsets in the bitmap.   
Using percentages allows for the possibility that the image is zoomed. */   
StartPixelX = MulDiv(LeadBitmap.GetWidth(), StartGDIX - rLeadDest.left, DisplayWidth);   
StartPixelY = MulDiv(LeadBitmap.GetHeight(), StartGDIY - rLeadDest.top, DisplayHeight);   
/* Initialize a variable used when the WM_MOUSEMOVE event outlines the area */   
FirstDraw = TRUE;