fix a crash in getImageDate if the rectangle is outside the canvas

CHANGELOG.md

@@ -13,6 +13,8 @@ project adheres to [Semantic Versioning](http://semver.org/).
 * Add missing property `canvas` to the `CanvasRenderingContext2D` type
 * Fixed glyph positions getting rounded, resulting text having a slight `letter-spacing` effect
 * Fixed `ctx.font` not being restored correctly after `ctx.restore()` (#1946)
+* Fix a crash in `getImageData` when the rectangle is entirely outside the canvas. ([#2024](https://github.com/Automattic/node-canvas/issues/2024))
+* Fix `getImageData` cropping the resulting `ImageData` when the given rectangle is partly outside the canvas. ([#1849](https://github.com/Automattic/node-canvas/issues/1849))
 
 2.11.0
 ==================

src/CanvasRenderingContext2d.cc

@@ -989,21 +989,26 @@ NAN_METHOD(Context2d::GetImageData) {
  sh = -sh;
  }
 
- if (sx + sw > width) sw = width - sx;
- if (sy + sh > height) sh = height - sy;
-
- // WebKit/moz functionality. node-canvas used to return in either case.
- if (sw <= 0) sw = 1;
- if (sh <= 0) sh = 1;
-
- // Non-compliant. "Pixels outside the canvas must be returned as transparent
- // black." This instead clips the returned array to the canvas area.
+ // Width and height to actually copy
+ int cw = sw;
+ int ch = sh;
+ // Offsets in the destination image
+ int ox = 0;
+ int oy = 0;
+
+ // Clamp the copy width and height if the copy would go outside the image
+ if (sx + sw > width) cw = width - sx;
+ if (sy + sh > height) ch = height - sy;
+
+ // Clamp the copy origin if the copy would go outside the image
  if (sx < 0) {
- sw += sx;
+ ox = -sx;
+ cw += sx;
  sx = 0;
  }
  if (sy < 0) {
- sh += sy;
+ oy = -sy;
+ ch += sy;
  sy = 0;
  }
 
@@ -1026,93 +1031,98 @@ NAN_METHOD(Context2d::GetImageData) {
  Nan::TypedArrayContents<uint8_t> typedArrayContents(dataArray);
  uint8_t* dst = *typedArrayContents;
 
- switch (canvas->backend()->getFormat()) {
- case CAIRO_FORMAT_ARGB32: {
- // Rearrange alpha (argb -> rgba), undo alpha pre-multiplication,
- // and store in big-endian format
- for (int y = 0; y < sh; ++y) {
- uint32_t *row = (uint32_t *)(src + srcStride * (y + sy));
- for (int x = 0; x < sw; ++x) {
- int bx = x * 4;
- uint32_t *pixel = row + x + sx;
- uint8_t a = *pixel >> 24;
- uint8_t r = *pixel >> 16;
- uint8_t g = *pixel >> 8;
- uint8_t b = *pixel;
- dst[bx + 3] = a;
-
- // Performance optimization: fully transparent/opaque pixels can be
- // processed more efficiently.
- if (a == 0 || a == 255) {
+ if (cw > 0 && ch > 0) {
+ switch (canvas->backend()->getFormat()) {
+ case CAIRO_FORMAT_ARGB32: {
+ dst += oy * dstStride + ox * 4;
+ // Rearrange alpha (argb -> rgba), undo alpha pre-multiplication,
+ // and store in big-endian format
+ for (int y = 0; y < ch; ++y) {
+ uint32_t *row = (uint32_t *)(src + srcStride * (y + sy));
+ for (int x = 0; x < cw; ++x) {
+ int bx = x * 4;
+ uint32_t *pixel = row + x + sx;
+ uint8_t a = *pixel >> 24;
+ uint8_t r = *pixel >> 16;
+ uint8_t g = *pixel >> 8;
+ uint8_t b = *pixel;
+ dst[bx + 3] = a;
+
+ // Performance optimization: fully transparent/opaque pixels can be
+ // processed more efficiently.
+ if (a == 0 || a == 255) {
+ dst[bx + 0] = r;
+ dst[bx + 1] = g;
+ dst[bx + 2] = b;
+ } else {
+ // Undo alpha pre-multiplication
+ float alphaR = (float)255 / a;
+ dst[bx + 0] = (int)((float)r * alphaR);
+ dst[bx + 1] = (int)((float)g * alphaR);
+ dst[bx + 2] = (int)((float)b * alphaR);
+ }
+ }
+ dst += dstStride;
+ }
+ break;
+ }
+ case CAIRO_FORMAT_RGB24: {
+ dst += oy * dstStride + ox * 4;
+ // Rearrange alpha (argb -> rgba) and store in big-endian format
+ for (int y = 0; y < ch; ++y) {
+ uint32_t *row = (uint32_t *)(src + srcStride * (y + sy));
+ for (int x = 0; x < cw; ++x) {
+ int bx = x * 4;
+ uint32_t *pixel = row + x + sx;
+ uint8_t r = *pixel >> 16;
+ uint8_t g = *pixel >> 8;
+ uint8_t b = *pixel;
+
  dst[bx + 0] = r;
  dst[bx + 1] = g;
  dst[bx + 2] = b;
- } else {
- // Undo alpha pre-multiplication
- float alphaR = (float)255 / a;
- dst[bx + 0] = (int)((float)r * alphaR);
- dst[bx + 1] = (int)((float)g * alphaR);
- dst[bx + 2] = (int)((float)b * alphaR);
+ dst[bx + 3] = 255;
  }
-
+ dst += dstStride;
  }
- dst += dstStride;
- }
- break;
- }
- case CAIRO_FORMAT_RGB24: {
- // Rearrange alpha (argb -> rgba) and store in big-endian format
- for (int y = 0; y < sh; ++y) {
- uint32_t *row = (uint32_t *)(src + srcStride * (y + sy));
- for (int x = 0; x < sw; ++x) {
- int bx = x * 4;
- uint32_t *pixel = row + x + sx;
- uint8_t r = *pixel >> 16;
- uint8_t g = *pixel >> 8;
- uint8_t b = *pixel;
-
- dst[bx + 0] = r;
- dst[bx + 1] = g;
- dst[bx + 2] = b;
- dst[bx + 3] = 255;
+ break;
  }
- dst += dstStride;
+ case CAIRO_FORMAT_A8: {
+ dst += oy * dstStride + ox;
+ for (int y = 0; y < ch; ++y) {
+ uint8_t *row = (uint8_t *)(src + srcStride * (y + sy));
+ memcpy(dst, row + sx, cw);
+ dst += dstStride;
+ }
+ break;
  }
- break;
- }
- case CAIRO_FORMAT_A8: {
- for (int y = 0; y < sh; ++y) {
- uint8_t *row = (uint8_t *)(src + srcStride * (y + sy));
- memcpy(dst, row + sx, dstStride);
- dst += dstStride;
+ case CAIRO_FORMAT_A1: {
+ // TODO Should this be totally packed, or maintain a stride divisible by 4?
+ Nan::ThrowError("getImageData for CANVAS_FORMAT_A1 is not yet implemented");
+ break;
  }
- break;
- }
- case CAIRO_FORMAT_A1: {
- // TODO Should this be totally packed, or maintain a stride divisible by 4?
- Nan::ThrowError("getImageData for CANVAS_FORMAT_A1 is not yet implemented");
- break;
- }
- case CAIRO_FORMAT_RGB16_565: {
- for (int y = 0; y < sh; ++y) {
- uint16_t *row = (uint16_t *)(src + srcStride * (y + sy));
- memcpy(dst, row + sx, dstStride);
- dst += dstStride;
+ case CAIRO_FORMAT_RGB16_565: {
+ dst += oy * dstStride + ox * 2;
+ for (int y = 0; y < ch; ++y) {
+ uint16_t *row = (uint16_t *)(src + srcStride * (y + sy));
+ memcpy(dst, row + sx, cw * 2);
+ dst += dstStride;
+ }
+ break;
  }
- break;
- }
 #ifdef CAIRO_FORMAT_RGB30
- case CAIRO_FORMAT_RGB30: {
- // TODO
- Nan::ThrowError("getImageData for CANVAS_FORMAT_RGB30 is not yet implemented");
- break;
- }
+  case CAIRO_FORMAT_RGB30: {
+  // TODO
+  Nan::ThrowError("getImageData for CANVAS_FORMAT_RGB30 is not yet implemented");
+  break;
+  }
 #endif
- default: {
- // Unlikely
- Nan::ThrowError("Invalid pixel format or not an image canvas");
- return;
- }
+ default: {
+ // Unlikely
+ Nan::ThrowError("Invalid pixel format or not an image canvas");
+ return;
+ }
+ }
  }
 
  const int argc = 3;