Q66305: _setcliprgn Does Not Work Inside a _setviewport

Article: Q66305
Product(s): See article
Version(s): 6.00 6.00a
Operating System(s): MS-DOS
Keyword(s): ENDUSER | s_quickc buglist6.00 buglist6.00a | mspl13_c
Last Modified: 19-JAN-1991

There is a conflict between the _setviewport() and _setcliprgn()
functions included in the graphics libraries in C versions 6.00 and
6.00a and QuickC versions 2.50 and 2.51. The _setcliprgn() function
should not affect the viewport coordinates, but using it after
_setviewport() causes changes in some graphics output.

The code below illustrates this problem. It draws an arc in the
upper-right corner of the window and then sets the clipping region
just inside the viewport; the program then draws the same arc again.
The second arc is shifted to the right and changed from the previous
arc.

Code Example
------------

#include <stdio.h>
#include <conio.h>
#include <graph.h>

void main(void)
{
    struct videoconfig vc;

    _setvideomode(_MAXRESMODE);
    _clearscreen(_GCLEARSCREEN);
    _getvideoconfig(&vc);
    _setviewport(55, 55, vc.numxpixels-55, vc.numypixels-55);
    _setwindow(1, 0.0, -10.0, 10.0, 10.0);
    _rectangle_w(_GBORDER, 0.0, -10.0, 10.0, 10.0);
    _ellipse_w(_GBORDER, 5.0, 5.0, 15.0, 15.0);
    _moveto(10,10);
    _outtext("Press any key to set a clipping region ");
    _outtext("and display the same arc...");
    getch();
    _setcliprgn(56, 56, vc.numxpixels-56, vc.numypixels-56);
    _ellipse_w(_GBORDER, 5.0, 5.0, 15.0, 15.0);
    getch();
    _setvideomode(_DEFAULTMODE);
}

Microsoft has confirmed this to be a problem with Microsoft C Compiler
versions 6.00 and 6.00a. We are researching this problem and will post
new information here as it becomes available.

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