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Fix off-by-one error in clipping_Xbitblt (#327)

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The LowerRightX and LowerRightY were calculated as the X and Y coordinates of the
pixel to the right and below the last visible pixel, but are compared with the
last actually visible pixel in the source. They need an extra -1 offset to correct.

Add comments to explain what's going on.  Fix the signature of the function to reflect
that the "dummy" passed for the display region is a pointer not an integer.
This commit is contained in:
Nick Briggs
2021-01-30 19:03:17 -08:00
committed by GitHub
parent 3764acda85
commit 1f17665741
2 changed files with 13 additions and 6 deletions
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2
inc/xbbtdefs.h
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@@ -1,4 +1,4 @@
#ifndef XBBTDEFS_H #ifndef XBBTDEFS_H
#define XBBTDEFS_H 1 #define XBBTDEFS_H 1
unsigned long clipping_Xbitblt(DspInterface dsp, int dummy, int x, int y, int w, int h); unsigned long clipping_Xbitblt(DspInterface dsp, DLword *dummy, int x, int y, int w, int h);
#endif #endif

17
src/xbbt.c
View File

@@ -30,20 +30,23 @@
/* dummy is the placeholder for the bitmap to be blitted */ /* dummy is the placeholder for the bitmap to be blitted */
/* */ /* */
/************************************************************************/ /************************************************************************/
unsigned long clipping_Xbitblt(DspInterface dsp, int dummy, int x, int y, int w, int h) unsigned long clipping_Xbitblt(DspInterface dsp, DLword *dummy, int x, int y, int w, int h)
{ {
int temp_x, temp_y, LowerRightX, LowerRightY; int temp_x, temp_y, LowerRightX, LowerRightY;
LowerRightX = dsp->Visible.x + dsp->Visible.width; LowerRightX = dsp->Visible.x + dsp->Visible.width - 1;
LowerRightY = dsp->Visible.y + dsp->Visible.height; LowerRightY = dsp->Visible.y + dsp->Visible.height - 1;
/* display region of interest lower right x, y pixel */
temp_x = x + w - 1; temp_x = x + w - 1;
temp_y = y + h - 1; temp_y = y + h - 1;
/* if the display region of interest is completely outside the visible window */
if ((temp_x < dsp->Visible.x) || (x > LowerRightX) || (temp_y < dsp->Visible.y) || if ((temp_x < dsp->Visible.x) || (x > LowerRightX) || (temp_y < dsp->Visible.y) ||
(y > LowerRightY)) (y > LowerRightY))
return (0); return (0);
/* if the display region of interest is completely within the visible window */
if ((x >= dsp->Visible.x) && (temp_x <= LowerRightX) && (y >= dsp->Visible.y) && if ((x >= dsp->Visible.x) && (temp_x <= LowerRightX) && (y >= dsp->Visible.y) &&
(temp_y <= LowerRightY)) { (temp_y <= LowerRightY)) {
XLOCK; XLOCK;
@@ -51,21 +54,25 @@ unsigned long clipping_Xbitblt(DspInterface dsp, int dummy, int x, int y, int w,
x - dsp->Visible.x, y - dsp->Visible.y, w, h); x - dsp->Visible.x, y - dsp->Visible.y, w, h);
XFlush(dsp->display_id); XFlush(dsp->display_id);
XUNLOCK; XUNLOCK;
return (0); return (1);
} }
/* clip left to visible window */
if (x < dsp->Visible.x) { if (x < dsp->Visible.x) {
w -= dsp->Visible.x - x; w -= dsp->Visible.x - x;
x = dsp->Visible.x; x = dsp->Visible.x;
} }
/* clip right to visible window */
if (temp_x > LowerRightX) w -= temp_x - LowerRightX; if (temp_x > LowerRightX) w -= temp_x - LowerRightX;
/* clip top to visible window */
if (y < dsp->Visible.y) { if (y < dsp->Visible.y) {
h -= dsp->Visible.y - y; h -= dsp->Visible.y - y;
y = dsp->Visible.y; y = dsp->Visible.y;
} }
/* clip bottom to visible window */
if (temp_y > LowerRightY) h -= temp_y - LowerRightY; if (temp_y > LowerRightY) h -= temp_y - LowerRightY;
if ((w > 0) && (h > 0)) { if ((w > 0) && (h > 0)) {
@@ -75,6 +82,6 @@ unsigned long clipping_Xbitblt(DspInterface dsp, int dummy, int x, int y, int w,
XFlush(dsp->display_id); XFlush(dsp->display_id);
XUNLOCK; XUNLOCK;
} }
return (0); return (1);
} /* end clipping_Xbitblt */ } /* end clipping_Xbitblt */