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* Copyright 2010 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef GrClip_DEFINED
#define GrClip_DEFINED
#include "include/core/SkRRect.h"
#include "include/core/SkRect.h"
#include "src/gpu/GrAppliedClip.h"
#include "src/gpu/GrSurfaceDrawContext.h"
* GrClip is an abstract base class for applying a clip. It constructs a clip mask if necessary, and
* fills out a GrAppliedClip instructing the caller on how to set up the draw state.
class GrClip {
enum class Effect {
// The clip conservatively modifies the draw's coverage but doesn't eliminate the draw
// The clip definitely does not modify the draw's coverage and the draw can be performed
// without clipping (beyond the automatic device bounds clip).
// The clip definitely eliminates all of the draw's coverage and the draw can be skipped
struct PreClipResult {
Effect fEffect;
SkRRect fRRect; // Ignore if 'isRRect' is false
GrAA fAA; // Ignore if 'isRRect' is false
bool fIsRRect;
PreClipResult(Effect effect) : fEffect(effect), fIsRRect(false) {}
PreClipResult(SkRect rect, GrAA aa) : PreClipResult(SkRRect::MakeRect(rect), aa) {}
PreClipResult(SkRRect rrect, GrAA aa)
: fEffect(Effect::kClipped)
, fRRect(rrect)
, fAA(aa)
, fIsRRect(true) {}
virtual ~GrClip() {}
* Compute a conservative pixel bounds restricted to the given render target dimensions.
* The returned bounds represent the limits of pixels that can be drawn; anything outside of the
* bounds will be entirely clipped out.
virtual SkIRect getConservativeBounds() const = 0;
* This computes a GrAppliedClip from the clip which in turn can be used to build a GrPipeline.
* To determine the appropriate clipping implementation the GrClip subclass must know whether
* the draw will enable HW AA or uses the stencil buffer. On input 'bounds' is a conservative
* bounds of the draw that is to be clipped. If kClipped or kUnclipped is returned, the 'bounds'
* will have been updated to be contained within the clip bounds (or the device's, for wide-open
* clips). If kNoDraw is returned, 'bounds' and the applied clip are in an undetermined state
* and should be ignored (and the draw should be skipped).
virtual Effect apply(GrRecordingContext*, GrSurfaceDrawContext*, GrAAType,
bool hasUserStencilSettings, GrAppliedClip*, SkRect* bounds) const = 0;
* Perform preliminary, conservative analysis on the draw bounds as if it were provided to
* apply(). The results of this are returned the PreClipResults struct, where 'result.fEffect'
* corresponds to what 'apply' would return. If this value is kUnclipped or kNoDraw, then it
* can be assumed that apply() would also always result in the same Effect.
* If kClipped is returned, apply() may further refine the effect to kUnclipped or kNoDraw,
* with one exception. When 'result.fIsRRect' is true, preApply() reports the single round rect
* and anti-aliased state that would act as an intersection on the draw geometry. If no further
* action is taken to modify the draw, apply() will represent this round rect in the applied
* clip.
* When set, 'result.fRRect' will intersect with the render target bounds but may extend
* beyond it. If the render target bounds are the only clip effect on the draw, this is reported
* as kUnclipped and not as a degenerate rrect that matches the bounds.
virtual PreClipResult preApply(const SkRect& drawBounds, GrAA aa) const {
SkIRect pixelBounds = GetPixelIBounds(drawBounds, aa);
bool outside = !SkIRect::Intersects(pixelBounds, this->getConservativeBounds());
return outside ? Effect::kClippedOut : Effect::kClipped;
* This is the maximum distance that a draw may extend beyond a clip's boundary and still count
* count as "on the other side". We leave some slack because floating point rounding error is
* likely to blame. The rationale for 1e-3 is that in the coverage case (and barring unexpected
* rounding), as long as coverage stays within 0.5 * 1/256 of its intended value it shouldn't
* have any effect on the final pixel values.
constexpr static SkScalar kBoundsTolerance = 1e-3f;
* This is the slack around a half-pixel vertex coordinate where we don't trust the GPU's
* rasterizer to round consistently. The rounding method is not defined in GPU specs, and
* rasterizer precision frequently introduces errors where a fraction < 1/2 still rounds up.
* For non-AA bounds edges, an edge value between 0.45 and 0.55 will round in or round out
* depending on what side its on. Outside of this range, the non-AA edge will snap using round()
constexpr static SkScalar kHalfPixelRoundingTolerance = 5e-2f;
* Returns true if the given query bounds count as entirely inside the clip.
* DEPRECATED: Only used by GrReducedClip
* @param innerClipBounds device-space rect contained by the clip (SkRect or SkIRect).
* @param queryBounds device-space bounds of the query region.
template <typename TRect>
constexpr static bool IsInsideClip(const TRect& innerClipBounds, const SkRect& queryBounds) {
return innerClipBounds.fRight > innerClipBounds.fLeft + kBoundsTolerance &&
innerClipBounds.fBottom > innerClipBounds.fTop + kBoundsTolerance &&
innerClipBounds.fLeft < queryBounds.fLeft + kBoundsTolerance &&
innerClipBounds.fTop < queryBounds.fTop + kBoundsTolerance &&
innerClipBounds.fRight > queryBounds.fRight - kBoundsTolerance &&
innerClipBounds.fBottom > queryBounds.fBottom - kBoundsTolerance;
* Returns true if the given query bounds count as entirely outside the clip.
* DEPRECATED: Only used by GrReducedClip
* @param outerClipBounds device-space rect that contains the clip (SkRect or SkIRect).
* @param queryBounds device-space bounds of the query region.
template <typename TRect>
constexpr static bool IsOutsideClip(const TRect& outerClipBounds, const SkRect& queryBounds) {
// Is the clip so small that it is effectively empty?
outerClipBounds.fRight - outerClipBounds.fLeft <= kBoundsTolerance ||
outerClipBounds.fBottom - outerClipBounds.fTop <= kBoundsTolerance ||
// Are the query bounds effectively outside the clip?
outerClipBounds.fLeft >= queryBounds.fRight - kBoundsTolerance ||
outerClipBounds.fTop >= queryBounds.fBottom - kBoundsTolerance ||
outerClipBounds.fRight <= queryBounds.fLeft + kBoundsTolerance ||
outerClipBounds.fBottom <= queryBounds.fTop + kBoundsTolerance;
// Modifies the behavior of GetPixelIBounds
enum class BoundsType {
* Returns the tightest integer pixel bounding box such that the rasterization of a shape
* contained in the analytic 'bounds', using the 'aa' method, will only have non-zero
* coverage for pixels inside the returned bounds. Pixels outside the bounds will either
* not be touched, or will have 0 coverage that creates no visual change.
* Returns the largest integer pixel bounding box such that were 'bounds' to be rendered as
* a solid fill using 'aa', every pixel in the returned bounds will have full coverage.
* This effectively determines the pixels that are definitely covered by a draw or clip. It
* effectively performs the opposite operations as GetOuterPixelBounds. It rounds in instead
* of out for coverage AA and non-AA near pixel centers.
* Returns the minimal integer rect that counts as containing a given set of bounds.
* DEPRECATED: Only used by GrReducedClip
static SkIRect GetPixelIBounds(const SkRect& bounds) {
return GetPixelIBounds(bounds, GrAA::kYes);
* Convert the analytic bounds of a shape into an integer pixel bounds, where the given aa type
* is used when the shape is rendered. The bounds mode can be used to query exterior or interior
* pixel boundaries. Interior bounds only make sense when its know that the analytic bounds
* are filled completely.
* NOTE: When using kExterior_Bounds, some coverage-AA rendering methods may still touch a pixel
* center outside of these bounds but will evaluate to 0 coverage. This is visually acceptable,
* but an additional outset of 1px should be used for dst proxy access.
static SkIRect GetPixelIBounds(const SkRect& bounds, GrAA aa,
BoundsType mode = BoundsType::kExterior) {
auto roundLow = [aa](float v) {
v += kBoundsTolerance;
return aa == GrAA::kNo ? SkScalarRoundToInt(v - kHalfPixelRoundingTolerance)
: SkScalarFloorToInt(v);
auto roundHigh = [aa](float v) {
v -= kBoundsTolerance;
return aa == GrAA::kNo ? SkScalarRoundToInt(v + kHalfPixelRoundingTolerance)
: SkScalarCeilToInt(v);
if (bounds.isEmpty()) {
return SkIRect::MakeEmpty();
if (mode == BoundsType::kExterior) {
return SkIRect::MakeLTRB(roundLow(bounds.fLeft), roundLow(bounds.fTop),
roundHigh(bounds.fRight), roundHigh(bounds.fBottom));
} else {
return SkIRect::MakeLTRB(roundHigh(bounds.fLeft), roundHigh(bounds.fTop),
roundLow(bounds.fRight), roundLow(bounds.fBottom));
* Returns the minimal pixel-aligned rect that counts as containing a given set of bounds.
* DEPRECATED: Only used by GrReducedClip
static SkRect GetPixelBounds(const SkRect& bounds) {
return SkRect::MakeLTRB(SkScalarFloorToScalar(bounds.fLeft + kBoundsTolerance),
SkScalarFloorToScalar(bounds.fTop + kBoundsTolerance),
SkScalarCeilToScalar(bounds.fRight - kBoundsTolerance),
SkScalarCeilToScalar(bounds.fBottom - kBoundsTolerance));
* Returns true if the given rect counts as aligned with pixel boundaries.
static bool IsPixelAligned(const SkRect& rect) {
return SkScalarAbs(SkScalarRoundToScalar(rect.fLeft) - rect.fLeft) <= kBoundsTolerance &&
SkScalarAbs(SkScalarRoundToScalar(rect.fTop) - rect.fTop) <= kBoundsTolerance &&
SkScalarAbs(SkScalarRoundToScalar(rect.fRight) - rect.fRight) <= kBoundsTolerance &&
SkScalarAbs(SkScalarRoundToScalar(rect.fBottom) - rect.fBottom) <= kBoundsTolerance;
* GrHardClip never uses coverage FPs. It can only enforce the clip using the already-existing
* stencil buffer contents and/or fixed-function state like scissor. Always aliased if MSAA is off.
class GrHardClip : public GrClip {
* Sets the appropriate hardware state modifications on GrAppliedHardClip that will implement
* the clip. On input 'bounds' is a conservative bounds of the draw that is to be clipped. After
* return 'bounds' has been intersected with a conservative bounds of the clip.
virtual Effect apply(GrAppliedHardClip* out, SkIRect* bounds) const = 0;
Effect apply(GrRecordingContext*, GrSurfaceDrawContext* rtc, GrAAType aa,
bool hasUserStencilSettings, GrAppliedClip* out, SkRect* bounds) const final {
SkIRect pixelBounds = GetPixelIBounds(*bounds, GrAA(aa != GrAAType::kNone));
Effect effect = this->apply(&out->hardClip(), &pixelBounds);
return effect;