| /* |
| * Copyright 2011 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #include "SkLineClipper.h" |
| |
| template <typename T> T pin_unsorted(T value, T limit0, T limit1) { |
| if (limit1 < limit0) { |
| SkTSwap(limit0, limit1); |
| } |
| // now the limits are sorted |
| SkASSERT(limit0 <= limit1); |
| |
| if (value < limit0) { |
| value = limit0; |
| } else if (value > limit1) { |
| value = limit1; |
| } |
| return value; |
| } |
| |
| // return X coordinate of intersection with horizontal line at Y |
| static SkScalar sect_with_horizontal(const SkPoint src[2], SkScalar Y) { |
| SkScalar dy = src[1].fY - src[0].fY; |
| if (SkScalarNearlyZero(dy)) { |
| return SkScalarAve(src[0].fX, src[1].fX); |
| } else { |
| // need the extra precision so we don't compute a value that exceeds |
| // our original limits |
| double X0 = src[0].fX; |
| double Y0 = src[0].fY; |
| double X1 = src[1].fX; |
| double Y1 = src[1].fY; |
| double result = X0 + ((double)Y - Y0) * (X1 - X0) / (Y1 - Y0); |
| |
| // The computed X value might still exceed [X0..X1] due to quantum flux |
| // when the doubles were added and subtracted, so we have to pin the |
| // answer :( |
| return (float)pin_unsorted(result, X0, X1); |
| } |
| } |
| |
| // return Y coordinate of intersection with vertical line at X |
| static SkScalar sect_with_vertical(const SkPoint src[2], SkScalar X) { |
| SkScalar dx = src[1].fX - src[0].fX; |
| if (SkScalarNearlyZero(dx)) { |
| return SkScalarAve(src[0].fY, src[1].fY); |
| } else { |
| // need the extra precision so we don't compute a value that exceeds |
| // our original limits |
| double X0 = src[0].fX; |
| double Y0 = src[0].fY; |
| double X1 = src[1].fX; |
| double Y1 = src[1].fY; |
| double result = Y0 + ((double)X - X0) * (Y1 - Y0) / (X1 - X0); |
| return (float)result; |
| } |
| } |
| |
| /////////////////////////////////////////////////////////////////////////////// |
| |
| static inline bool nestedLT(SkScalar a, SkScalar b, SkScalar dim) { |
| return a <= b && (a < b || dim > 0); |
| } |
| |
| // returns true if outer contains inner, even if inner is empty. |
| // note: outer.contains(inner) always returns false if inner is empty. |
| static inline bool containsNoEmptyCheck(const SkRect& outer, |
| const SkRect& inner) { |
| return outer.fLeft <= inner.fLeft && outer.fTop <= inner.fTop && |
| outer.fRight >= inner.fRight && outer.fBottom >= inner.fBottom; |
| } |
| |
| bool SkLineClipper::IntersectLine(const SkPoint src[2], const SkRect& clip, |
| SkPoint dst[2]) { |
| SkRect bounds; |
| |
| bounds.set(src[0], src[1]); |
| if (containsNoEmptyCheck(clip, bounds)) { |
| if (src != dst) { |
| memcpy(dst, src, 2 * sizeof(SkPoint)); |
| } |
| return true; |
| } |
| // check for no overlap, and only permit coincident edges if the line |
| // and the edge are colinear |
| if (nestedLT(bounds.fRight, clip.fLeft, bounds.width()) || |
| nestedLT(clip.fRight, bounds.fLeft, bounds.width()) || |
| nestedLT(bounds.fBottom, clip.fTop, bounds.height()) || |
| nestedLT(clip.fBottom, bounds.fTop, bounds.height())) { |
| return false; |
| } |
| |
| int index0, index1; |
| |
| if (src[0].fY < src[1].fY) { |
| index0 = 0; |
| index1 = 1; |
| } else { |
| index0 = 1; |
| index1 = 0; |
| } |
| |
| SkPoint tmp[2]; |
| memcpy(tmp, src, sizeof(tmp)); |
| |
| // now compute Y intersections |
| if (tmp[index0].fY < clip.fTop) { |
| tmp[index0].set(sect_with_horizontal(src, clip.fTop), clip.fTop); |
| } |
| if (tmp[index1].fY > clip.fBottom) { |
| tmp[index1].set(sect_with_horizontal(src, clip.fBottom), clip.fBottom); |
| } |
| |
| if (tmp[0].fX < tmp[1].fX) { |
| index0 = 0; |
| index1 = 1; |
| } else { |
| index0 = 1; |
| index1 = 0; |
| } |
| |
| // check for quick-reject in X again, now that we may have been chopped |
| if ((tmp[index1].fX <= clip.fLeft || tmp[index0].fX >= clip.fRight) && |
| tmp[index0].fX < tmp[index1].fX) { |
| // only reject if we have a non-zero width |
| return false; |
| } |
| |
| if (tmp[index0].fX < clip.fLeft) { |
| tmp[index0].set(clip.fLeft, sect_with_vertical(src, clip.fLeft)); |
| } |
| if (tmp[index1].fX > clip.fRight) { |
| tmp[index1].set(clip.fRight, sect_with_vertical(src, clip.fRight)); |
| } |
| #ifdef SK_DEBUG |
| bounds.set(tmp[0], tmp[1]); |
| SkASSERT(containsNoEmptyCheck(clip, bounds)); |
| #endif |
| memcpy(dst, tmp, sizeof(tmp)); |
| return true; |
| } |
| |
| #ifdef SK_DEBUG |
| // return value between the two limits, where the limits are either ascending |
| // or descending. |
| static bool is_between_unsorted(SkScalar value, |
| SkScalar limit0, SkScalar limit1) { |
| if (limit0 < limit1) { |
| return limit0 <= value && value <= limit1; |
| } else { |
| return limit1 <= value && value <= limit0; |
| } |
| } |
| #endif |
| |
| int SkLineClipper::ClipLine(const SkPoint pts[], const SkRect& clip, SkPoint lines[], |
| bool canCullToTheRight) { |
| int index0, index1; |
| |
| if (pts[0].fY < pts[1].fY) { |
| index0 = 0; |
| index1 = 1; |
| } else { |
| index0 = 1; |
| index1 = 0; |
| } |
| |
| // Check if we're completely clipped out in Y (above or below |
| |
| if (pts[index1].fY <= clip.fTop) { // we're above the clip |
| return 0; |
| } |
| if (pts[index0].fY >= clip.fBottom) { // we're below the clip |
| return 0; |
| } |
| |
| // Chop in Y to produce a single segment, stored in tmp[0..1] |
| |
| SkPoint tmp[2]; |
| memcpy(tmp, pts, sizeof(tmp)); |
| |
| // now compute intersections |
| if (pts[index0].fY < clip.fTop) { |
| tmp[index0].set(sect_with_horizontal(pts, clip.fTop), clip.fTop); |
| SkASSERT(is_between_unsorted(tmp[index0].fX, pts[0].fX, pts[1].fX)); |
| } |
| if (tmp[index1].fY > clip.fBottom) { |
| tmp[index1].set(sect_with_horizontal(pts, clip.fBottom), clip.fBottom); |
| SkASSERT(is_between_unsorted(tmp[index1].fX, pts[0].fX, pts[1].fX)); |
| } |
| |
| // Chop it into 1..3 segments that are wholly within the clip in X. |
| |
| // temp storage for up to 3 segments |
| SkPoint resultStorage[kMaxPoints]; |
| SkPoint* result; // points to our results, either tmp or resultStorage |
| int lineCount = 1; |
| bool reverse; |
| |
| if (pts[0].fX < pts[1].fX) { |
| index0 = 0; |
| index1 = 1; |
| reverse = false; |
| } else { |
| index0 = 1; |
| index1 = 0; |
| reverse = true; |
| } |
| |
| if (tmp[index1].fX <= clip.fLeft) { // wholly to the left |
| tmp[0].fX = tmp[1].fX = clip.fLeft; |
| result = tmp; |
| reverse = false; |
| } else if (tmp[index0].fX >= clip.fRight) { // wholly to the right |
| if (canCullToTheRight) { |
| return 0; |
| } |
| tmp[0].fX = tmp[1].fX = clip.fRight; |
| result = tmp; |
| reverse = false; |
| } else { |
| result = resultStorage; |
| SkPoint* r = result; |
| |
| if (tmp[index0].fX < clip.fLeft) { |
| r->set(clip.fLeft, tmp[index0].fY); |
| r += 1; |
| r->set(clip.fLeft, sect_with_vertical(tmp, clip.fLeft)); |
| SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY)); |
| } else { |
| *r = tmp[index0]; |
| } |
| r += 1; |
| |
| if (tmp[index1].fX > clip.fRight) { |
| r->set(clip.fRight, sect_with_vertical(tmp, clip.fRight)); |
| SkASSERT(is_between_unsorted(r->fY, tmp[0].fY, tmp[1].fY)); |
| r += 1; |
| r->set(clip.fRight, tmp[index1].fY); |
| } else { |
| *r = tmp[index1]; |
| } |
| |
| lineCount = SkToInt(r - result); |
| } |
| |
| // Now copy the results into the caller's lines[] parameter |
| if (reverse) { |
| // copy the pts in reverse order to maintain winding order |
| for (int i = 0; i <= lineCount; i++) { |
| lines[lineCount - i] = result[i]; |
| } |
| } else { |
| memcpy(lines, result, (lineCount + 1) * sizeof(SkPoint)); |
| } |
| return lineCount; |
| } |
