/* -*- Mode: C++; tab-width: 20; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "gfxXlibNativeRenderer.h"

#include "gfxXlibSurface.h"
#include "gfxImageSurface.h"
#include "gfxContext.h"
#include "gfxPlatform.h"
#include "gfxAlphaRecovery.h"
#include "cairo-xlib.h"
#include "cairo-xlib-xrender.h"
#include "mozilla/gfx/BorrowedContext.h"

using namespace mozilla;
using namespace mozilla::gfx;

#if 0
#include <stdio.h>
#define NATIVE_DRAWING_NOTE(m) fprintf(stderr, m)
#else
#define NATIVE_DRAWING_NOTE(m) do {} while (0)
#endif

/* We have four basic strategies available:

   1) 'direct': If the target is an xlib surface, and other conditions are met,
      we can pass the underlying drawable directly to the callback.

   2) 'simple': If the drawing is opaque, or we can draw to a surface with an
      alpha channel, then we can create a temporary xlib surface, pass its
      underlying drawable to the callback, and composite the result using
      cairo.

   3) 'copy-background': If the drawing is not opaque but the target is
      opaque, and we can draw to a surface with format such that pixel
      conversion to and from the target format is exact, we can create a
      temporary xlib surface, copy the background from the target, pass the
      underlying drawable to the callback, and copy back to the target.

      This strategy is not used if the pixel format conversion is not exact,
      because that would mean that drawing intended to be very transparent
      messes with other content.

      The strategy is prefered over simple for non-opaque drawing and opaque
      targets on the same screen as compositing without alpha is a simpler
      operation.

   4) 'alpha-extraction': create a temporary xlib surface, fill with black,
      pass its underlying drawable to the callback, copy the results to a
      cairo image surface, repeat with a white background, update the on-black
      image alpha values by comparing the two images, then paint the on-black
      image using cairo.

      Sure would be nice to have an X extension or GL to do this for us on the
      server...
*/

static cairo_bool_t
_convert_coord_to_int (double coord, int32_t *v)
{
    *v = (int32_t)coord;
    /* XXX allow some tolerance here? */
    return *v == coord;
}

static bool
_get_rectangular_clip (cairo_t *cr,
                       const nsIntRect& bounds,
                       bool *need_clip,
                       nsIntRect *rectangles, int max_rectangles,
                       int *num_rectangles)
{
    cairo_rectangle_list_t *cliplist;
    cairo_rectangle_t *clips;
    int i;
    bool retval = true;

    cliplist = cairo_copy_clip_rectangle_list (cr);
    if (cliplist->status != CAIRO_STATUS_SUCCESS) {
        retval = false;
        NATIVE_DRAWING_NOTE("FALLBACK: non-rectangular clip");
        goto FINISH;
    }

    /* the clip is always in surface backend coordinates (i.e. native backend coords) */
    clips = cliplist->rectangles;

    for (i = 0; i < cliplist->num_rectangles; ++i) {
        
        nsIntRect rect;
        if (!_convert_coord_to_int (clips[i].x, &rect.x) ||
            !_convert_coord_to_int (clips[i].y, &rect.y) ||
            !_convert_coord_to_int (clips[i].width, &rect.width) ||
            !_convert_coord_to_int (clips[i].height, &rect.height))
        {
            retval = false;
            NATIVE_DRAWING_NOTE("FALLBACK: non-integer clip");
            goto FINISH;
        }

        if (rect.IsEqualInterior(bounds)) {
            /* the bounds are entirely inside the clip region so we don't need to clip. */
            *need_clip = false;
            goto FINISH;
        }            

        NS_ASSERTION(bounds.Contains(rect),
                     "Was expecting to be clipped to bounds");

        if (i >= max_rectangles) {
            retval = false;
            NATIVE_DRAWING_NOTE("FALLBACK: unsupported clip rectangle count");
            goto FINISH;
        }

        rectangles[i] = rect;
    }
  
    *need_clip = true;
    *num_rectangles = cliplist->num_rectangles;

FINISH:
    cairo_rectangle_list_destroy (cliplist);

    return retval;
}

#define MAX_STATIC_CLIP_RECTANGLES 50

/**
 * Try the direct path.
 * @return True if we took the direct path
 */
bool
gfxXlibNativeRenderer::DrawDirect(gfxContext *ctx, nsIntSize size,
                                  uint32_t flags,
                                  Screen *screen, Visual *visual)
{
    if (ctx->IsCairo()) {
        return DrawCairo(ctx->GetCairo(), size, flags, screen, visual);
    }

    // We need to actually borrow the context because we want to read out the
    // clip rectangles.
    BorrowedCairoContext borrowed(ctx->GetDrawTarget());
    if (!borrowed.mCairo) {
      return false;
    }

    bool direct = DrawCairo(borrowed.mCairo, size, flags, screen, visual);
    borrowed.Finish();

    return direct;
}

bool
gfxXlibNativeRenderer::DrawCairo(cairo_t* cr, nsIntSize size,
                                 uint32_t flags,
                                 Screen *screen, Visual *visual)
{
    /* Check that the target surface is an xlib surface. */
    cairo_surface_t *target = cairo_get_group_target (cr);
    if (cairo_surface_get_type (target) != CAIRO_SURFACE_TYPE_XLIB) {
        NATIVE_DRAWING_NOTE("FALLBACK: non-X surface");
        return false;
    }

    cairo_matrix_t matrix;
    cairo_get_matrix (cr, &matrix);
    double device_offset_x, device_offset_y;
    cairo_surface_get_device_offset (target, &device_offset_x, &device_offset_y);

    /* Draw() checked that the matrix contained only a very-close-to-integer
       translation.  Here (and in several other places and thebes) device
       offsets are assumed to be integer. */
    NS_ASSERTION(int32_t(device_offset_x) == device_offset_x &&
                 int32_t(device_offset_y) == device_offset_y,
                 "Expected integer device offsets");
    nsIntPoint offset(NS_lroundf(matrix.x0 + device_offset_x),
                      NS_lroundf(matrix.y0 + device_offset_y));

    int max_rectangles = 0;
    if (flags & DRAW_SUPPORTS_CLIP_RECT) {
      max_rectangles = 1;
    }
    if (flags & DRAW_SUPPORTS_CLIP_LIST) {
      max_rectangles = MAX_STATIC_CLIP_RECTANGLES;
    }

    /* The client won't draw outside the surface so consider this when
       analysing clip rectangles. */
    nsIntRect bounds(offset, size);
    bounds.IntersectRect(bounds,
                         nsIntRect(0, 0,
                                   cairo_xlib_surface_get_width(target),
                                   cairo_xlib_surface_get_height(target)));

    bool needs_clip = true;
    nsIntRect rectangles[MAX_STATIC_CLIP_RECTANGLES];
    int rect_count = 0;

    /* Check that the clip is rectangular and aligned on unit boundaries. */
    /* Temporarily set the matrix for _get_rectangular_clip. It's basically
       the identity matrix, but we must adjust for the fact that our
       offset-rect is in device coordinates. */
    cairo_identity_matrix (cr);
    cairo_translate (cr, -device_offset_x, -device_offset_y);
    bool have_rectangular_clip =
        _get_rectangular_clip (cr, bounds, &needs_clip,
                               rectangles, max_rectangles, &rect_count);
    cairo_set_matrix (cr, &matrix);
    if (!have_rectangular_clip)
        return false;

    /* Stop now if everything is clipped out */
    if (needs_clip && rect_count == 0)
        return true;

    /* Check that the screen is supported.
       Visuals belong to screens, so, if alternate visuals are not supported,
       then alternate screens cannot be supported. */
    bool supports_alternate_visual =
        (flags & DRAW_SUPPORTS_ALTERNATE_VISUAL) != 0;
    bool supports_alternate_screen = supports_alternate_visual &&
        (flags & DRAW_SUPPORTS_ALTERNATE_SCREEN);
    if (!supports_alternate_screen &&
        cairo_xlib_surface_get_screen (target) != screen) {
        NATIVE_DRAWING_NOTE("FALLBACK: non-default screen");
        return false;
    }

    /* Check that there is a visual */
    Visual *target_visual = cairo_xlib_surface_get_visual (target);
    if (!target_visual) {
        NATIVE_DRAWING_NOTE("FALLBACK: no Visual for surface");
        return false;
    }
    /* Check that the visual is supported */
    if (!supports_alternate_visual && target_visual != visual) {
        // Only the format of the visual is important (not the GLX properties)
        // for Xlib or XRender drawing.
        XRenderPictFormat *target_format =
            cairo_xlib_surface_get_xrender_format (target);
        if (!target_format ||
            (target_format !=
             XRenderFindVisualFormat (DisplayOfScreen(screen), visual))) {
            NATIVE_DRAWING_NOTE("FALLBACK: unsupported Visual");
            return false;
        }
    }

    /* we're good to go! */
    NATIVE_DRAWING_NOTE("TAKING FAST PATH\n");
    cairo_surface_flush (target);
    nsRefPtr<gfxASurface> surface = gfxASurface::Wrap(target);
    nsresult rv = DrawWithXlib(static_cast<gfxXlibSurface*>(surface.get()),
                               offset, rectangles,
                               needs_clip ? rect_count : 0);
    if (NS_SUCCEEDED(rv)) {
        cairo_surface_mark_dirty (target);
        return true;
    }
    return false;
}

static bool
VisualHasAlpha(Screen *screen, Visual *visual) {
    // There may be some other visuals format with alpha but usually this is
    // the only one we care about.
    return visual->c_class == TrueColor &&
        visual->bits_per_rgb == 8 &&
        visual->red_mask == 0xff0000 &&
        visual->green_mask == 0xff00 &&
        visual->blue_mask == 0xff &&
        gfxXlibSurface::DepthOfVisual(screen, visual) == 32;
}

// Returns whether pixel conversion between visual and format is exact (in
// both directions).
static bool
FormatConversionIsExact(Screen *screen, Visual *visual, XRenderPictFormat *format) {
    if (!format ||
        visual->c_class != TrueColor ||
        format->type != PictTypeDirect ||
        gfxXlibSurface::DepthOfVisual(screen, visual) != format->depth)
        return false;

    XRenderPictFormat *visualFormat =
        XRenderFindVisualFormat(DisplayOfScreen(screen), visual);

    if (visualFormat->type != PictTypeDirect )
        return false;

    const XRenderDirectFormat& a = visualFormat->direct;
    const XRenderDirectFormat& b = format->direct;
    return a.redMask == b.redMask &&
        a.greenMask == b.greenMask &&
        a.blueMask == b.blueMask;
}

// The 3 non-direct strategies described above.
// The surface format and strategy are inter-dependent.
enum DrawingMethod {
    eSimple,
    eCopyBackground,
    eAlphaExtraction
};

static already_AddRefed<gfxXlibSurface>
CreateTempXlibSurface (gfxASurface *destination, nsIntSize size,
                       bool canDrawOverBackground,
                       uint32_t flags, Screen *screen, Visual *visual,
                       DrawingMethod *method)
{
    bool drawIsOpaque = (flags & gfxXlibNativeRenderer::DRAW_IS_OPAQUE) != 0;
    bool supportsAlternateVisual =
        (flags & gfxXlibNativeRenderer::DRAW_SUPPORTS_ALTERNATE_VISUAL) != 0;
    bool supportsAlternateScreen = supportsAlternateVisual &&
        (flags & gfxXlibNativeRenderer::DRAW_SUPPORTS_ALTERNATE_SCREEN);

    cairo_surface_t *target = destination->CairoSurface();
    cairo_surface_type_t target_type = cairo_surface_get_type (target);
    cairo_content_t target_content = cairo_surface_get_content (target);

    Screen *target_screen = target_type == CAIRO_SURFACE_TYPE_XLIB ?
        cairo_xlib_surface_get_screen (target) : screen;

    // When the background has an alpha channel, we need to draw with an alpha
    // channel anyway, so there is no need to copy the background.  If
    // doCopyBackground is set here, we'll also need to check below that the
    // background can copied without any loss in format conversions.
    bool doCopyBackground = !drawIsOpaque && canDrawOverBackground &&
        target_content == CAIRO_CONTENT_COLOR;

    if (supportsAlternateScreen && screen != target_screen && drawIsOpaque) {
        // Prefer a visual on the target screen.
        // (If !drawIsOpaque, we'll need doCopyBackground or an alpha channel.)
        visual = DefaultVisualOfScreen(target_screen);
        screen = target_screen;

    } else if (doCopyBackground || (supportsAlternateVisual && drawIsOpaque)) {
        // Analyse the pixel formats either to check whether we can
        // doCopyBackground or to see if we can find a better visual for
        // opaque drawing.
        Visual *target_visual = nullptr;
        XRenderPictFormat *target_format = nullptr;
        switch (target_type) {
        case CAIRO_SURFACE_TYPE_XLIB:
            target_visual = cairo_xlib_surface_get_visual (target);
            target_format = cairo_xlib_surface_get_xrender_format (target);
            break;
        case CAIRO_SURFACE_TYPE_IMAGE: {
            gfxImageFormat imageFormat =
                static_cast<gfxImageSurface*>(destination)->Format();
            target_visual = gfxXlibSurface::FindVisual(screen, imageFormat);
            Display *dpy = DisplayOfScreen(screen);
            if (target_visual) {
                target_format = XRenderFindVisualFormat(dpy, target_visual);
            } else {
                target_format =
                    gfxXlibSurface::FindRenderFormat(dpy, imageFormat);
            }                
            break;
        }
        default:
            break;
        }

        if (supportsAlternateVisual &&
            (supportsAlternateScreen || screen == target_screen)) {
            if (target_visual) {
                visual = target_visual;
                screen = target_screen;
            }
        }
        // Could try harder to match formats across screens for background
        // copying when !supportsAlternateScreen, if we cared.  Preferably
        // we'll find a visual below with an alpha channel anyway; if so, the
        // background won't need to be copied.

        if (doCopyBackground && visual != target_visual &&
            !FormatConversionIsExact(screen, visual, target_format)) {
            doCopyBackground = false;
        }
    }

    if (supportsAlternateVisual && !drawIsOpaque &&
        (screen != target_screen ||
         !(doCopyBackground || VisualHasAlpha(screen, visual)))) {
        // Try to find a visual with an alpha channel.
        Screen *visualScreen =
            supportsAlternateScreen ? target_screen : screen;
        Visual *argbVisual =
            gfxXlibSurface::FindVisual(visualScreen,
                                       gfxImageFormatARGB32);
        if (argbVisual) {
            visual = argbVisual;
            screen = visualScreen;
        } else if (!doCopyBackground &&
                   gfxXlibSurface::DepthOfVisual(screen, visual) != 24) {
            // Will need to do alpha extraction; prefer a 24-bit visual.
            // No advantage in using the target screen.
            Visual *rgb24Visual =
                gfxXlibSurface::FindVisual(screen,
                                           gfxImageFormatRGB24);
            if (rgb24Visual) {
                visual = rgb24Visual;
            }
        }
    }

    Drawable drawable =
        (screen == target_screen && target_type == CAIRO_SURFACE_TYPE_XLIB) ?
        cairo_xlib_surface_get_drawable (target) : RootWindowOfScreen(screen);

    nsRefPtr<gfxXlibSurface> surface =
        gfxXlibSurface::Create(screen, visual,
                               gfxIntSize(size.width, size.height),
                               drawable);

    if (drawIsOpaque ||
        surface->GetContentType() == GFX_CONTENT_COLOR_ALPHA) {
        NATIVE_DRAWING_NOTE(drawIsOpaque ?
                            ", SIMPLE OPAQUE\n" : ", SIMPLE WITH ALPHA");
        *method = eSimple;
    } else if (doCopyBackground) {
        NATIVE_DRAWING_NOTE(", COPY BACKGROUND\n");
        *method = eCopyBackground;
    } else {
        NATIVE_DRAWING_NOTE(", SLOW ALPHA EXTRACTION\n");
        *method = eAlphaExtraction;
    }

    return surface.forget();
}

bool
gfxXlibNativeRenderer::DrawOntoTempSurface(gfxXlibSurface *tempXlibSurface,
                                           nsIntPoint offset)
{
    tempXlibSurface->Flush();
    /* no clipping is needed because the callback can't draw outside the native
       surface anyway */
    nsresult rv = DrawWithXlib(tempXlibSurface, offset, nullptr, 0);
    tempXlibSurface->MarkDirty();
    return NS_SUCCEEDED(rv);
}

static already_AddRefed<gfxImageSurface>
CopyXlibSurfaceToImage(gfxXlibSurface *tempXlibSurface,
                       gfxImageFormat format)
{
    nsRefPtr<gfxImageSurface> result =
        new gfxImageSurface(tempXlibSurface->GetSize(), format);

    gfxContext copyCtx(result);
    copyCtx.SetSource(tempXlibSurface);
    copyCtx.SetOperator(gfxContext::OPERATOR_SOURCE);
    copyCtx.Paint();

    return result.forget();
}

void
gfxXlibNativeRenderer::Draw(gfxContext* ctx, nsIntSize size,
                            uint32_t flags, Screen *screen, Visual *visual,
                            DrawOutput* result)
{
    if (result) {
        result->mSurface = nullptr;
        result->mUniformAlpha = false;
        result->mUniformColor = false;
    }

    gfxMatrix matrix = ctx->CurrentMatrix();

    // We can only draw direct or onto a copied background if pixels align and
    // native drawing is compatible with the current operator.  (The matrix is
    // actually also pixel-exact for flips and right-angle rotations, which
    // would permit copying the background but not drawing direct.)
    bool matrixIsIntegerTranslation = !matrix.HasNonIntegerTranslation();
    bool canDrawOverBackground = matrixIsIntegerTranslation &&
        ctx->CurrentOperator() == gfxContext::OPERATOR_OVER;

    // The padding of 0.5 for non-pixel-exact transformations used here is
    // the same as what _cairo_pattern_analyze_filter uses.
    const gfxFloat filterRadius = 0.5;
    gfxRect affectedRect(0.0, 0.0, size.width, size.height);
    if (!matrixIsIntegerTranslation) {
        // The filter footprint means that the affected rectangle is a
        // little larger than the drawingRect;
        affectedRect.Inflate(filterRadius);

        NATIVE_DRAWING_NOTE("FALLBACK: matrix not integer translation");
    } else if (!canDrawOverBackground) {
        NATIVE_DRAWING_NOTE("FALLBACK: unsupported operator");
    }

    // Clipping to the region affected by drawing allows us to consider only
    // the portions of the clip region that will be affected by drawing.
    gfxRect clipExtents;
    {
        gfxContextAutoSaveRestore autoSR(ctx);
        ctx->Clip(affectedRect);

        clipExtents = ctx->GetClipExtents();
        if (clipExtents.IsEmpty())
            return; // nothing to do

        if (canDrawOverBackground &&
            DrawDirect(ctx, size, flags, screen, visual))
          return;
    }

    nsIntRect drawingRect(nsIntPoint(0, 0), size);
    // Drawing need only be performed within the clip extents
    // (and padding for the filter).
    if (!matrixIsIntegerTranslation) {
        // The source surface may need to be a little larger than the clip
        // extents due to the filter footprint.
        clipExtents.Inflate(filterRadius);
    }
    clipExtents.RoundOut();

    nsIntRect intExtents(int32_t(clipExtents.X()),
                         int32_t(clipExtents.Y()),
                         int32_t(clipExtents.Width()),
                         int32_t(clipExtents.Height()));
    drawingRect.IntersectRect(drawingRect, intExtents);

    if (ctx->IsCairo()) {
        nsRefPtr<gfxASurface> target(ctx->CurrentSurface());
        DrawFallback(nullptr, ctx, target, size, drawingRect, canDrawOverBackground,
                     flags, screen, visual, result);
    } else {
        DrawTarget* drawTarget = ctx->GetDrawTarget();
        if (!drawTarget) {
            return;
        }

        nsRefPtr<gfxASurface> target = gfxPlatform::GetPlatform()->
            GetThebesSurfaceForDrawTarget(drawTarget);
        if (!target) {
            return;
        }
        DrawFallback(drawTarget, ctx, target, size, drawingRect, canDrawOverBackground,
                     flags, screen, visual, result);
    }
}

void
gfxXlibNativeRenderer::DrawFallback(DrawTarget* drawTarget, gfxContext* ctx, gfxASurface* target,
                                    nsIntSize& size, nsIntRect& drawingRect,
                                    bool canDrawOverBackground, uint32_t flags,
                                    Screen* screen, Visual* visual, DrawOutput* result)
{
    gfxPoint offset(drawingRect.x, drawingRect.y);

    DrawingMethod method;
    nsRefPtr<gfxXlibSurface> tempXlibSurface = 
        CreateTempXlibSurface(target, drawingRect.Size(),
                              canDrawOverBackground, flags, screen, visual,
                              &method);
    if (!tempXlibSurface)
        return;

    if (drawingRect.Size() != size || method == eCopyBackground) {
        // Only drawing a portion, or copying background,
        // so won't return a result.
        result = nullptr;
    }
  
    nsRefPtr<gfxContext> tmpCtx;
    bool drawIsOpaque = (flags & DRAW_IS_OPAQUE) != 0;
    if (!drawIsOpaque) {
        tmpCtx = new gfxContext(tempXlibSurface);
        if (method == eCopyBackground) {
            tmpCtx->SetOperator(gfxContext::OPERATOR_SOURCE);
            tmpCtx->SetSource(target, -(offset + ctx->CurrentMatrix().GetTranslation()));
            // The copy from the tempXlibSurface to the target context should
            // use operator SOURCE, but that would need a mask to bound the
            // operation.  Here we only copy opaque backgrounds so operator
            // OVER will behave like SOURCE masked by the surface.
            NS_ASSERTION(tempXlibSurface->GetContentType()
                         == GFX_CONTENT_COLOR,
                         "Don't copy background with a transparent surface");
        } else {
            tmpCtx->SetOperator(gfxContext::OPERATOR_CLEAR);
        }
        tmpCtx->Paint();
    }

    if (!DrawOntoTempSurface(tempXlibSurface, -drawingRect.TopLeft())) {
        return;
    }
  
    if (method != eAlphaExtraction) {
        if (drawTarget) {
            RefPtr<SourceSurface> sourceSurface = gfxPlatform::GetPlatform()->
                GetSourceSurfaceForSurface(drawTarget, tempXlibSurface);
            drawTarget->DrawSurface(sourceSurface,
                Rect(offset.x, offset.y, size.width, size.height),
                Rect(0, 0, size.width, size.height));
        } else {
            ctx->SetSource(tempXlibSurface, offset);
            ctx->Paint();
        }
        if (result) {
            result->mSurface = tempXlibSurface;
            /* fill in the result with what we know, which is really just what our
               assumption was */
            result->mUniformAlpha = true;
            result->mColor.a = 1.0;
        }
        return;
    }
    
    nsRefPtr<gfxImageSurface> blackImage =
        CopyXlibSurfaceToImage(tempXlibSurface, gfxImageFormatARGB32);
    
    tmpCtx->SetDeviceColor(gfxRGBA(1.0, 1.0, 1.0));
    tmpCtx->SetOperator(gfxContext::OPERATOR_SOURCE);
    tmpCtx->Paint();
    DrawOntoTempSurface(tempXlibSurface, -drawingRect.TopLeft());
    nsRefPtr<gfxImageSurface> whiteImage =
        CopyXlibSurfaceToImage(tempXlibSurface, gfxImageFormatRGB24);
  
    if (blackImage->CairoStatus() == CAIRO_STATUS_SUCCESS &&
        whiteImage->CairoStatus() == CAIRO_STATUS_SUCCESS) {
        gfxAlphaRecovery::Analysis analysis;
        if (!gfxAlphaRecovery::RecoverAlpha(blackImage, whiteImage,
                                            result ? &analysis : nullptr))
            return;

        gfxASurface* paintSurface = blackImage;
        /* if the caller wants to retrieve the rendered image, put it into
           a 'similar' surface, and use that as the source for the drawing right
           now. This means we always return a surface similar to the surface
           used for 'cr', which is ideal if it's going to be cached and reused.
           We do not return an image if the result has uniform color (including
           alpha). */
        if (result) {
            if (analysis.uniformAlpha) {
                result->mUniformAlpha = true;
                result->mColor.a = analysis.alpha;
            }
            if (analysis.uniformColor) {
                result->mUniformColor = true;
                result->mColor.r = analysis.r;
                result->mColor.g = analysis.g;
                result->mColor.b = analysis.b;
            } else {
                result->mSurface = target->
                    CreateSimilarSurface(GFX_CONTENT_COLOR_ALPHA,
                                         gfxIntSize(size.width, size.height));

                gfxContext copyCtx(result->mSurface);
                copyCtx.SetSource(blackImage);
                copyCtx.SetOperator(gfxContext::OPERATOR_SOURCE);
                copyCtx.Paint();

                paintSurface = result->mSurface;
            }
        }
        if (drawTarget) {
            RefPtr<SourceSurface> sourceSurface = gfxPlatform::GetPlatform()->
                GetSourceSurfaceForSurface(drawTarget, paintSurface);
            drawTarget->DrawSurface(sourceSurface,
                Rect(offset.x, offset.y, size.width, size.height),
                Rect(0, 0, size.width, size.height));
        } else {
            ctx->SetSource(paintSurface, offset);
            ctx->Paint();
        }
    }
}