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140 lines
4.5 KiB
C
140 lines
4.5 KiB
C
/* $TOG: miscanfill.h /main/6 1998/02/09 14:48:35 kaleb $ */
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/*
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Copyright 1987, 1998 The Open Group
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All Rights Reserved.
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The above copyright notice and this permission notice shall be included
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in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
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OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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IN NO EVENT SHALL THE OPEN GROUP BE LIABLE FOR ANY CLAIM, DAMAGES OR
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OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
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ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
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OTHER DEALINGS IN THE SOFTWARE.
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Except as contained in this notice, the name of The Open Group shall
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not be used in advertising or otherwise to promote the sale, use or
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other dealings in this Software without prior written authorization
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from The Open Group.
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*/
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#ifndef SCANFILLINCLUDED
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#define SCANFILLINCLUDED
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/*
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* scanfill.h
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*
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* Written by Brian Kelleher; Jan 1985
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*
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* This file contains a few macros to help track
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* the edge of a filled object. The object is assumed
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* to be filled in scanline order, and thus the
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* algorithm used is an extension of Bresenham's line
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* drawing algorithm which assumes that y is always the
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* major axis.
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* Since these pieces of code are the same for any filled shape,
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* it is more convenient to gather the library in one
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* place, but since these pieces of code are also in
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* the inner loops of output primitives, procedure call
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* overhead is out of the question.
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* See the author for a derivation if needed.
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*/
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/*
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* In scan converting polygons, we want to choose those pixels
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* which are inside the polygon. Thus, we add .5 to the starting
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* x coordinate for both left and right edges. Now we choose the
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* first pixel which is inside the pgon for the left edge and the
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* first pixel which is outside the pgon for the right edge.
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* Draw the left pixel, but not the right.
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*
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* How to add .5 to the starting x coordinate:
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* If the edge is moving to the right, then subtract dy from the
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* error term from the general form of the algorithm.
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* If the edge is moving to the left, then add dy to the error term.
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*
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* The reason for the difference between edges moving to the left
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* and edges moving to the right is simple: If an edge is moving
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* to the right, then we want the algorithm to flip immediately.
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* If it is moving to the left, then we don't want it to flip until
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* we traverse an entire pixel.
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*/
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#define BRESINITPGON(dy, x1, x2, xStart, d, m, m1, incr1, incr2) { \
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int dx; /* local storage */ \
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\
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/* \
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* if the edge is horizontal, then it is ignored \
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* and assumed not to be processed. Otherwise, do this stuff. \
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*/ \
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if ((dy) != 0) { \
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xStart = (x1); \
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dx = (x2) - xStart; \
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if (dx < 0) { \
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m = dx / (dy); \
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m1 = m - 1; \
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incr1 = -2 * dx + 2 * (dy) * m1; \
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incr2 = -2 * dx + 2 * (dy) * m; \
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d = 2 * m * (dy) - 2 * dx - 2 * (dy); \
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} else { \
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m = dx / (dy); \
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m1 = m + 1; \
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incr1 = 2 * dx - 2 * (dy) * m1; \
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incr2 = 2 * dx - 2 * (dy) * m; \
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d = -2 * m * (dy) + 2 * dx; \
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} \
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} \
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}
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#define BRESINCRPGON(d, minval, m, m1, incr1, incr2) { \
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if (m1 > 0) { \
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if (d > 0) { \
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minval += m1; \
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d += incr1; \
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} \
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else { \
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minval += m; \
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d += incr2; \
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} \
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} else {\
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if (d >= 0) { \
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minval += m1; \
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d += incr1; \
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} \
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else { \
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minval += m; \
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d += incr2; \
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} \
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} \
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}
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/*
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* This structure contains all of the information needed
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* to run the bresenham algorithm.
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* The variables may be hardcoded into the declarations
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* instead of using this structure to make use of
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* register declarations.
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*/
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typedef struct {
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int minor; /* minor axis */
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int d; /* decision variable */
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int m, m1; /* slope and slope+1 */
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int incr1, incr2; /* error increments */
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} BRESINFO;
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#define BRESINITPGONSTRUCT(dmaj, min1, min2, bres) \
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BRESINITPGON(dmaj, min1, min2, bres.minor, bres.d, \
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bres.m, bres.m1, bres.incr1, bres.incr2)
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#define BRESINCRPGONSTRUCT(bres) \
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BRESINCRPGON(bres.d, bres.minor, bres.m, bres.m1, bres.incr1, bres.incr2)
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#endif
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