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I don't understand fixed point arithmetic - this fixed that, I hope

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This commit is contained in:
Amy Bowersox 2019-12-10 14:30:45 -07:00
parent d66aa4de24
commit 3996501cf0
1 changed files with 27 additions and 21 deletions
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48
src/devctxt.c
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@ -5,7 +5,7 @@
#include "gfxobj.h" #include "gfxobj.h"
#include "devctxt.h" #include "devctxt.h"
inline static BYTE line_clip_outcode(INT64 x, INT64 y, INT64 xmin, INT64 ymin, INT64 xmax, INT64 ymax) inline static BYTE line_clip_outcode(INT32 x, INT32 y, INT32 xmin, INT32 ymin, INT32 xmax, INT32 ymax)
{ {
BYTE rc = 0; BYTE rc = 0;
if (y < ymin) if (y < ymin)
@ -19,13 +19,19 @@ inline static BYTE line_clip_outcode(INT64 x, INT64 y, INT64 xmin, INT64 ymin, I
return rc; return rc;
} }
static BOOL line_clip(PINT32 output, INT64 x1, INT64 y1, INT64 x2, INT64 y2, INT64 xmin, INT64 ymin, INT64 xmax, INT64 ymax) #define CPX 16 /* clipping precision in bits */
/* these macros keep the number of bits straight when doing fixed-point multiply & divide */
#define M(a, b) ((((a) * (b))) >> CPX)
#define D(a, b) (((a) << CPX) / (b))
static BOOL line_clip(PINT32 output, INT32 x1, INT32 y1, INT32 x2, INT32 y2, INT32 xmin, INT32 ymin, INT32 xmax, INT32 ymax)
{ {
BYTE outcode1, outcode2; BYTE outcode1, outcode2;
INT64 tmp; INT32 tmp;
Log(LDEBUG, "clipping line from (%lld, %lld) to (%lld, %lld) against bounding box (%lld, %lld, %lld, %lld)", x1 >> 16, y1 >> 16, x2 >> 16, y2 >> 16, Log(LDEBUG, "clipping line from (%d, %d) to (%d, %d) against bounding box (%d, %d, %d, %d)", x1 >> CPX, y1 >> CPX, x2 >> CPX, y2 >> CPX,
xmin >> 16, ymin >> 16, xmax >> 16, ymax >> 16); xmin >> CPX, ymin >> CPX, xmax >> CPX, ymax >> CPX);
/* Cohen-Sutherland line-clipping algorithm (see Foley & Van Dam, pp. 145-149) */ /* Cohen-Sutherland line-clipping algorithm (see Foley & Van Dam, pp. 145-149) */
for (;;) for (;;)
@ -55,47 +61,47 @@ static BOOL line_clip(PINT32 output, INT64 x1, INT64 y1, INT64 x2, INT64 y2, INT
} }
if (outcode1 & 0x8) if (outcode1 & 0x8)
{ {
tmp = (x2 - x1) * ((ymin - y1) / (y2 - y1)); tmp = M(x2 - x1, D(ymin - y1, y2 - y1));
x1 += tmp; x1 += tmp;
y1 = ymin; y1 = ymin;
Log(LDEBUG, "clipped against top to point (%lld, %lld), dx=%lld/%lld", x1 >> 16, y1 >> 16, tmp >> 16, tmp); Log(LDEBUG, "clipped against top to point (%d, %d), dx=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
} }
else if (outcode1 & 0x4) else if (outcode1 & 0x4)
{ {
tmp = (x2 - x1) * ((ymax - y1) / (y2 - y1)); tmp = M(x2 - x1, D(ymax - y1, y2 - y1));
x1 += tmp; x1 += tmp;
y1 = ymax; y1 = ymax;
Log(LDEBUG, "clipped against bottom to point (%lld, %lld), dx=%lld/%lld", x1 >> 16, y1 >> 16, tmp >> 16, tmp); Log(LDEBUG, "clipped against bottom to point (%d, %d), dx=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
} }
else if (outcode1 & 0x2) else if (outcode1 & 0x2)
{ {
tmp = (y2 - y1) * ((xmax - x1) / (x2 - x1)); tmp = M(y2 - y1, D(xmax - x1, x2 - x1));
y1 -= tmp; y1 -= tmp;
x1 = xmax; x1 = xmax;
Log(LDEBUG, "clipped against right to point (%lld, %lld), dy=%lld/%lld", x1 >> 16, y1 >> 16, tmp >> 16, tmp); Log(LDEBUG, "clipped against right to point (%d, %d), dy=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
} }
else if (outcode1 & 0x1) else if (outcode1 & 0x1)
{ {
tmp = (y2 - y1) * ((xmin - x1) / (x2 - x1)); tmp = M(y2 - y1, D(xmin - x1, x2 - x1));
y1 -= tmp; y1 -= tmp;
x1 = xmin; x1 = xmin;
Log(LDEBUG, "clipped against left to point (%lld, %lld), dy=%lld/%lld", x1 >> 16, y1 >> 16, tmp >> 16, tmp); Log(LDEBUG, "clipped against left to point (%d, %d), dy=%d/%d", x1 >> CPX, y1 >> CPX, tmp >> CPX, tmp);
} }
} }
Log(LDEBUG, "final line is from (%lld, %lld) to (%lld, %lld)", x1 >> 16, y1 >> 16, x2 >> 16, y2 >> 16); Log(LDEBUG, "final line is from (%d, %d) to (%d, %d)", x1 >> CPX, y1 >> CPX, x2 >> CPX, y2 >> CPX);
output[0] = (INT32)x1; output[0] = x1;
output[1] = (INT32)y1; output[1] = y1;
output[2] = (INT32)x2; output[2] = x2;
output[3] = (INT32)y2; output[3] = y2;
return TRUE; return TRUE;
} }
static BOOL internal_line(PDCTXT pdctxt, INT32 x1, INT32 y1, INT32 x2, INT32 y2) static BOOL internal_line(PDCTXT pdctxt, INT32 x1, INT32 y1, INT32 x2, INT32 y2)
{ {
INT32 buffer[4]; INT32 buffer[4];
if (line_clip(buffer, x1 << 16, y1 << 16, x2 << 16, y2 << 16, pdctxt->cliprect.left << 16, pdctxt->cliprect.top << 16, if (line_clip(buffer, x1 << CPX, y1 << CPX, x2 << CPX, y2 << CPX, pdctxt->cliprect.left << CPX, pdctxt->cliprect.top << CPX,
pdctxt->cliprect.right << 16, pdctxt->cliprect.bottom << 16)) pdctxt->cliprect.right << CPX, pdctxt->cliprect.bottom << CPX))
return (*pdctxt->funcs->line)(pdctxt->privdata, buffer[0] >> 16, buffer[1] >> 16, buffer[2] >> 16, buffer[3] >> 16, pdctxt->color, pdctxt->rop2); return (*pdctxt->funcs->line)(pdctxt->privdata, buffer[0] >> CPX, buffer[1] >> CPX, buffer[2] >> CPX, buffer[3] >> CPX, pdctxt->color, pdctxt->rop2);
return TRUE; return TRUE;
} }