Rect Matrix4x4::ProjectRectBounds(const Rect& aRect) const
{
Point4D points[4];
points[0] = ProjectPoint(aRect.TopLeft());
points[1] = ProjectPoint(aRect.TopRight());
points[2] = ProjectPoint(aRect.BottomRight());
points[3] = ProjectPoint(aRect.BottomLeft());
Float min_x = std::numeric_limits<Float>::max();
Float min_y = std::numeric_limits<Float>::max();
Float max_x = -std::numeric_limits<Float>::max();
Float max_y = -std::numeric_limits<Float>::max();
bool foundPoint = false;
for (int i=0; i<4; i++) {
// Only use points that exist above the w=0 plane
if (points[i].HasPositiveWCoord()) {
foundPoint = true;
Point point2d = points[i].As2DPoint();
min_x = min<Float>(point2d.x, min_x);
max_x = max<Float>(point2d.x, max_x);
min_y = min<Float>(point2d.y, min_y);
max_y = max<Float>(point2d.y, max_y);
}
int next = (i == 3) ? 0 : i + 1;
if (points[i].HasPositiveWCoord() != points[next].HasPositiveWCoord()) {
// If the line between two points crosses the w=0 plane, then interpolate a point
// as close to the w=0 plane as possible and use that instead.
Point4D intercept = ComputePerspectivePlaneIntercept(points[i], points[next]);
Point point2d = intercept.As2DPoint();
min_x = min<Float>(point2d.x, min_x);
max_x = max<Float>(point2d.x, max_x);
min_y = min<Float>(point2d.y, min_y);
max_y = max<Float>(point2d.y, max_y);
}
}
if (!foundPoint) {
return Rect(0, 0, 0, 0);
}
return Rect(min_x, min_y, max_x - min_x, max_y - min_y);
}
Rect Matrix4x4::ProjectRectBounds(const Rect& aRect, const Rect &aClip) const
{
// This function must never return std::numeric_limits<Float>::max() or any
// other arbitrary large value in place of inifinity. This often occurs when
// aRect is an inversed projection matrix or when aRect is transformed to be
// partly behind and in front of the camera (w=0 plane in homogenous
// coordinates) - See Bug 1035611
// Some call-sites will call RoundGfxRectToAppRect which clips both the
// extents and dimensions of the rect to be bounded by nscoord_MAX.
// If we return a Rect that, when converted to nscoords, has a width or height
// greater than nscoord_MAX, RoundGfxRectToAppRect will clip the overflow
// off both the min and max end of the rect after clipping the extents of the
// rect, resulting in a translation of the rect towards the infinite end.
// The bounds returned by ProjectRectBounds are expected to be clipped only on
// the edges beyond the bounds of the coordinate system; otherwise, the
// clipped bounding box would be smaller than the correct one and result
// bugs such as incorrect culling (eg. Bug 1073056)
// To address this without requiring all code to work in homogenous
// coordinates or interpret infinite values correctly, a specialized
// clipping function is integrated into ProjectRectBounds.
// Callers should pass an aClip value that represents the extents to clip
// the result to, in the same coordinate system as aRect.
Point4D points[4];
points[0] = ProjectPoint(aRect.TopLeft());
points[1] = ProjectPoint(aRect.TopRight());
points[2] = ProjectPoint(aRect.BottomRight());
points[3] = ProjectPoint(aRect.BottomLeft());
Float min_x = std::numeric_limits<Float>::max();
Float min_y = std::numeric_limits<Float>::max();
Float max_x = -std::numeric_limits<Float>::max();
Float max_y = -std::numeric_limits<Float>::max();
for (int i=0; i<4; i++) {
// Only use points that exist above the w=0 plane
if (points[i].HasPositiveWCoord()) {
Point point2d = aClip.ClampPoint(points[i].As2DPoint());
min_x = std::min<Float>(point2d.x, min_x);
max_x = std::max<Float>(point2d.x, max_x);
min_y = std::min<Float>(point2d.y, min_y);
max_y = std::max<Float>(point2d.y, max_y);
}
int next = (i == 3) ? 0 : i + 1;
if (points[i].HasPositiveWCoord() != points[next].HasPositiveWCoord()) {
// If the line between two points crosses the w=0 plane, then interpolate
// to find the point of intersection with the w=0 plane and use that
// instead.
Point4D intercept = ComputePerspectivePlaneIntercept(points[i], points[next]);
// Since intercept.w will always be 0 here, we interpret x,y,z as a
// direction towards an infinite vanishing point.
if (intercept.x < 0.0f) {
min_x = aClip.x;
} else if (intercept.x > 0.0f) {
max_x = aClip.XMost();
}
if (intercept.y < 0.0f) {
min_y = aClip.y;
} else if (intercept.y > 0.0f) {
max_y = aClip.YMost();
}
}
}
if (max_x < min_x || max_y < min_y) {
return Rect(0, 0, 0, 0);
}
return Rect(min_x, min_y, max_x - min_x, max_y - min_y);
}
