/*
* 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, 2);
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, 2);
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
#ifdef SK_DEBUG
// This is an example of why we need to pin the result computed in
// sect_with_horizontal. If we didn't explicitly pin, is_between_unsorted would
// fail.
//
static void sect_with_horizontal_test_for_pin_results() {
const SkPoint pts[] = {
{ -540000, -720000 },
{ -9.10000017e-05f, 9.99999996e-13f }
};
float x = sect_with_horizontal(pts, 0);
SkASSERT(is_between_unsorted(x, pts[0].fX, pts[1].fX));
}
#endif
int SkLineClipper::ClipLine(const SkPoint pts[], const SkRect& clip,
SkPoint lines[]) {
#ifdef SK_DEBUG
{
static bool gOnce;
if (!gOnce) {
sect_with_horizontal_test_for_pin_results();
gOnce = true;
}
}
#endif
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
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;
}