Added an automated test for rectangle routines, currently only testing line clipping.
Use the Cohen-Sutherland algorithm for line clipping which uses integer math and preserves ordering of clipped points. Removed getopt() support in testsdl.c, replaced with simple argv scanning. --HG-- extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%404285
This commit is contained in:
Sam Lantinga
parent
4672f074e0
commit
1ba0c1618e
6 changed files with 305 additions and 268 deletions
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@ -196,16 +196,40 @@ SDL_EnclosePoints(const SDL_Point * points, int count, const SDL_Rect * clip,
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return SDL_TRUE;
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}
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/* Use the Cohen-Sutherland algorithm for line clipping */
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#define CODE_BOTTOM 1
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#define CODE_TOP 2
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#define CODE_LEFT 4
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#define CODE_RIGHT 8
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static int ComputeOutCode(const SDL_Rect * rect, int x, int y)
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{
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int code = 0;
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if (y < 0) {
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code |= CODE_TOP;
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} else if (y >= rect->y + rect->h) {
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code |= CODE_BOTTOM;
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}
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if (x < 0) {
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code |= CODE_LEFT;
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} else if (x >= rect->x + rect->w) {
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code |= CODE_RIGHT;
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}
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return code;
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}
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SDL_bool
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SDL_IntersectRectAndLine(const SDL_Rect * rect, int *X1, int *Y1, int *X2,
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int *Y2)
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{
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int x, y;
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int x1, y1;
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int x2, y2;
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int rectx1;
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int recty1;
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int rectx2;
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int recty2;
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int outcode1, outcode2;
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if (!rect || !X1 || !Y1 || !X2 || !Y2) {
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return SDL_FALSE;
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@ -262,95 +286,57 @@ SDL_IntersectRectAndLine(const SDL_Rect * rect, int *X1, int *Y1, int *X2,
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return SDL_TRUE;
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}
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else {
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/* The task of clipping a line with finite slope ratios in a fixed-
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* precision coordinate space is not as immediately simple as it is
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* with coordinates of arbitrary precision. If the ratio of slopes
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* between the input line segment and the result line segment is not
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* a whole number, you have in fact *moved* the line segment a bit,
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* and there can be no avoiding it without more precision
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*/
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int *x_result_[] = { X1, X2, NULL }, **x_result = x_result_;
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int *y_result_[] = { Y1, Y2, NULL }, **y_result = y_result_;
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SDL_bool intersection = SDL_FALSE;
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double b, m, left, right, bottom, top;
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int xl, xh, yl, yh;
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/* solve mx+b line formula */
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m = (double) (y1 - y2) / (double) (x1 - x2);
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b = y2 - m * (double) x2;
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/* find some linear intersections */
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left = (m * (double) rectx1) + b;
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right = (m * (double) rectx2) + b;
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top = (recty1 - b) / m;
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bottom = (recty2 - b) / m;
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/* sort end-points' x and y components individually */
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if (x1 < x2) {
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xl = x1;
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xh = x2;
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} else {
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xl = x2;
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xh = x1;
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}
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if (y1 < y2) {
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yl = y1;
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yh = y2;
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} else {
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yl = y2;
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yh = y1;
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/* More complicated Cohen-Sutherland algorithm */
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outcode1 = ComputeOutCode(rect, x1, y1);
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outcode2 = ComputeOutCode(rect, x2, y2);
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while (outcode1 || outcode2) {
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if (outcode1 & outcode2) {
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return SDL_FALSE;
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}
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#define RISING(a, b, c) (((a)<=(b))&&((b)<=(c)))
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/* check for a point that's entirely inside the rect */
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if (RISING(rectx1, x1, rectx2) && RISING(recty1, y1, recty2)) {
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x_result++;
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y_result++;
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intersection = SDL_TRUE;
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} else
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/* it was determined earlier that *both* end-points are not contained */
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if (RISING(rectx1, x2, rectx2) && RISING(recty1, y2, recty2)) {
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**(x_result++) = x2;
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**(y_result++) = y2;
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intersection = SDL_TRUE;
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if (outcode1) {
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if (outcode1 & CODE_TOP) {
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y = recty1;
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x = x1 + ((x2 - x1) * (y - y1)) / (y2 - y1);
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} else if (outcode1 & CODE_BOTTOM) {
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y = recty2;
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x = x1 + ((x2 - x1) * (y - y1)) / (y2 - y1);
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} else if (outcode1 & CODE_LEFT) {
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x = rectx1;
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y = y1 + ((y2 - y1) * (x - x1)) / (x2 - x1);
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} else if (outcode1 & CODE_RIGHT) {
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x = rectx2;
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y = y1 + ((y2 - y1) * (x - x1)) / (x2 - x1);
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}
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x1 = x;
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y1 = y;
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outcode1 = ComputeOutCode(rect, x, y);
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}
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if (RISING(recty1, left, recty2) && RISING(xl, rectx1, xh)) {
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**(x_result++) = rectx1;
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**(y_result++) = (int) left;
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intersection = SDL_TRUE;
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if (outcode2) {
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if (outcode2 & CODE_TOP) {
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y = recty1;
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x = x1 + ((x2 - x1) * (y - y1)) / (y2 - y1);
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} else if (outcode2 & CODE_BOTTOM) {
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y = recty2;
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x = x1 + ((x2 - x1) * (y - y1)) / (y2 - y1);
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} else if (outcode2 & CODE_LEFT) {
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x = rectx1;
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y = y1 + ((y2 - y1) * (x - x1)) / (x2 - x1);
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} else if (outcode2 & CODE_RIGHT) {
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x = rectx2;
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y = y1 + ((y2 - y1) * (x - x1)) / (x2 - x1);
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}
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x2 = x;
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y2 = y;
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outcode2 = ComputeOutCode(rect, x, y);
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}
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if (*x_result == NULL)
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return intersection;
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if (RISING(recty1, right, recty2) && RISING(xl, rectx2, xh)) {
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**(x_result++) = rectx2;
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**(y_result++) = (int) right;
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intersection = SDL_TRUE;
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}
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if (*x_result == NULL)
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return intersection;
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if (RISING(rectx1, top, rectx2) && RISING(yl, recty1, yh)) {
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**(x_result++) = (int) top;
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**(y_result++) = recty1;
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intersection = SDL_TRUE;
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}
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if (*x_result == NULL)
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return intersection;
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if (RISING(rectx1, bottom, rectx2) && RISING(yl, recty2, yh)) {
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**(x_result++) = (int) bottom;
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**(y_result++) = recty2;
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intersection = SDL_TRUE;
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}
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return intersection;
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}
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return SDL_FALSE;
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*X1 = x1;
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*Y1 = y1;
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*X2 = x2;
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*Y2 = y2;
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return SDL_TRUE;
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}
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void
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