summaryrefslogtreecommitdiffstats
path: root/gfx/2d
diff options
context:
space:
mode:
Diffstat (limited to 'gfx/2d')
-rw-r--r--gfx/2d/Matrix.h44
1 files changed, 29 insertions, 15 deletions
diff --git a/gfx/2d/Matrix.h b/gfx/2d/Matrix.h
index 22a01ca10..d6835c8e6 100644
--- a/gfx/2d/Matrix.h
+++ b/gfx/2d/Matrix.h
@@ -723,7 +723,7 @@ public:
* The resulting vertices are populated in aVerts. aVerts must be
* pre-allocated to hold at least kTransformAndClipRectMaxVerts Points.
* The vertex count is returned by TransformAndClipRect. It is possible to
- * emit fewer that 3 vertices, indicating that aRect will not be visible
+ * emit fewer than 3 vertices, indicating that aRect will not be visible
* within aClip.
*/
template<class F>
@@ -734,7 +734,8 @@ public:
// Initialize a double-buffered array of points in homogenous space with
// the input rectangle, aRect.
Point4DTyped<UnknownUnits, F> points[2][kTransformAndClipRectMaxVerts];
- Point4DTyped<UnknownUnits, F>* dstPoint = points[0];
+ Point4DTyped<UnknownUnits, F>* dstPointStart = points[0];
+ Point4DTyped<UnknownUnits, F>* dstPoint = dstPointStart;
*dstPoint++ = TransformPoint(Point4DTyped<UnknownUnits, F>(aRect.x, aRect.y, 0, 1));
*dstPoint++ = TransformPoint(Point4DTyped<UnknownUnits, F>(aRect.XMost(), aRect.y, 0, 1));
@@ -750,16 +751,26 @@ public:
planeNormals[3] = Point4DTyped<UnknownUnits, F>(0.0, -1.0, 0.0, aClip.YMost());
// Iterate through each clipping plane and clip the polygon.
- // In each pass, we double buffer, alternating between points[0] and
- // points[1].
+ // For each clipping plane, we intersect the plane with all polygon edges.
+ // Each pass can increase or decrease the number of points that make up the
+ // current clipped polygon. We double buffer that set of points, alternating
+ // between points[0] and points[1].
for (int plane=0; plane < 4; plane++) {
planeNormals[plane].Normalize();
- Point4DTyped<UnknownUnits, F>* srcPoint = points[plane & 1];
+ Point4DTyped<UnknownUnits, F>* srcPoint = dstPointStart;
Point4DTyped<UnknownUnits, F>* srcPointEnd = dstPoint;
- dstPoint = points[~plane & 1];
- Point4DTyped<UnknownUnits, F>* dstPointStart = dstPoint;
-
+ dstPointStart = points[~plane & 1];
+ dstPoint = dstPointStart;
+
+ // Iterate over the polygon edges. In each iteration the current edge is
+ // the edge from prevPoint to srcPoint. If the two end points lie on
+ // different sides of the plane, we have an intersection. Otherwise, the
+ // edge is either completely "inside" the half-space created by the
+ // clipping plane, and we add srcPoint, or it is completely "outside", and
+ // we discard srcPoint.
+ // We may create duplicated points in the polygon. We keep those around
+ // until all clipping is done and then filter out duplicates at the end.
Point4DTyped<UnknownUnits, F>* prevPoint = srcPointEnd - 1;
F prevDot = planeNormals[plane].DotProduct(*prevPoint);
while (srcPoint < srcPointEnd && ((dstPoint - dstPointStart) < kTransformAndClipRectMaxVerts)) {
@@ -783,14 +794,16 @@ public:
}
if (dstPoint == dstPointStart) {
+ // No polygon points were produced, so the polygon has been
+ // completely clipped away by the current clipping plane. Exit.
break;
}
}
- size_t dstPointCount = 0;
- size_t srcPointCount = dstPoint - points[0];
- for (Point4DTyped<UnknownUnits, F>* srcPoint = points[0]; srcPoint < points[0] + srcPointCount; srcPoint++) {
-
+ Point4DTyped<UnknownUnits, F>* srcPoint = dstPointStart;
+ Point4DTyped<UnknownUnits, F>* srcPointEnd = dstPoint;
+ size_t vertCount = 0;
+ while (srcPoint < srcPointEnd) {
PointTyped<TargetUnits, F> p;
if (srcPoint->w == 0.0) {
// If a point lies on the intersection of the clipping planes at
@@ -800,12 +813,13 @@ public:
p = srcPoint->As2DPoint();
}
// Emit only unique points
- if (dstPointCount == 0 || p != aVerts[dstPointCount - 1]) {
- aVerts[dstPointCount++] = p;
+ if (vertCount == 0 || p != aVerts[vertCount - 1]) {
+ aVerts[vertCount++] = p;
}
+ srcPoint++;
}
- return dstPointCount;
+ return vertCount;
}
static const int kTransformAndClipRectMaxVerts = 32;