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path: root/vendor/golang.org/x/image/bmp/reader.go
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Diffstat (limited to 'vendor/golang.org/x/image/bmp/reader.go')
-rw-r--r--vendor/golang.org/x/image/bmp/reader.go78
1 files changed, 55 insertions, 23 deletions
diff --git a/vendor/golang.org/x/image/bmp/reader.go b/vendor/golang.org/x/image/bmp/reader.go
index c10a022f6..e165c2e39 100644
--- a/vendor/golang.org/x/image/bmp/reader.go
+++ b/vendor/golang.org/x/image/bmp/reader.go
@@ -85,7 +85,7 @@ func decodeRGB(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
// decodeNRGBA reads a 32 bit-per-pixel BMP image from r.
// If topDown is false, the image rows will be read bottom-up.
-func decodeNRGBA(r io.Reader, c image.Config, topDown bool) (image.Image, error) {
+func decodeNRGBA(r io.Reader, c image.Config, topDown, allowAlpha bool) (image.Image, error) {
rgba := image.NewNRGBA(image.Rect(0, 0, c.Width, c.Height))
if c.Width == 0 || c.Height == 0 {
return rgba, nil
@@ -102,6 +102,9 @@ func decodeNRGBA(r io.Reader, c image.Config, topDown bool) (image.Image, error)
for i := 0; i < len(p); i += 4 {
// BMP images are stored in BGRA order rather than RGBA order.
p[i+0], p[i+2] = p[i+2], p[i+0]
+ if !allowAlpha {
+ p[i+3] = 0xFF
+ }
}
}
return rgba, nil
@@ -110,7 +113,7 @@ func decodeNRGBA(r io.Reader, c image.Config, topDown bool) (image.Image, error)
// Decode reads a BMP image from r and returns it as an image.Image.
// Limitation: The file must be 8, 24 or 32 bits per pixel.
func Decode(r io.Reader) (image.Image, error) {
- c, bpp, topDown, err := decodeConfig(r)
+ c, bpp, topDown, allowAlpha, err := decodeConfig(r)
if err != nil {
return nil, err
}
@@ -120,7 +123,7 @@ func Decode(r io.Reader) (image.Image, error) {
case 24:
return decodeRGB(r, c, topDown)
case 32:
- return decodeNRGBA(r, c, topDown)
+ return decodeNRGBA(r, c, topDown, allowAlpha)
}
panic("unreachable")
}
@@ -129,13 +132,15 @@ func Decode(r io.Reader) (image.Image, error) {
// decoding the entire image.
// Limitation: The file must be 8, 24 or 32 bits per pixel.
func DecodeConfig(r io.Reader) (image.Config, error) {
- config, _, _, err := decodeConfig(r)
+ config, _, _, _, err := decodeConfig(r)
return config, err
}
-func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown bool, err error) {
- // We only support those BMP images that are a BITMAPFILEHEADER
- // immediately followed by a BITMAPINFOHEADER.
+func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown bool, allowAlpha bool, err error) {
+ // We only support those BMP images with one of the following DIB headers:
+ // - BITMAPINFOHEADER (40 bytes)
+ // - BITMAPV4HEADER (108 bytes)
+ // - BITMAPV5HEADER (124 bytes)
const (
fileHeaderLen = 14
infoHeaderLen = 40
@@ -144,18 +149,24 @@ func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown b
)
var b [1024]byte
if _, err := io.ReadFull(r, b[:fileHeaderLen+4]); err != nil {
- return image.Config{}, 0, false, err
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ return image.Config{}, 0, false, false, err
}
if string(b[:2]) != "BM" {
- return image.Config{}, 0, false, errors.New("bmp: invalid format")
+ return image.Config{}, 0, false, false, errors.New("bmp: invalid format")
}
offset := readUint32(b[10:14])
infoLen := readUint32(b[14:18])
if infoLen != infoHeaderLen && infoLen != v4InfoHeaderLen && infoLen != v5InfoHeaderLen {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
if _, err := io.ReadFull(r, b[fileHeaderLen+4:fileHeaderLen+infoLen]); err != nil {
- return image.Config{}, 0, false, err
+ if err == io.EOF {
+ err = io.ErrUnexpectedEOF
+ }
+ return image.Config{}, 0, false, false, err
}
width := int(int32(readUint32(b[18:22])))
height := int(int32(readUint32(b[22:26])))
@@ -163,12 +174,12 @@ func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown b
height, topDown = -height, true
}
if width < 0 || height < 0 {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
// We only support 1 plane and 8, 24 or 32 bits per pixel and no
// compression.
planes, bpp, compression := readUint16(b[26:28]), readUint16(b[28:30]), readUint32(b[30:34])
- // if compression is set to BITFIELDS, but the bitmask is set to the default bitmask
+ // if compression is set to BI_BITFIELDS, but the bitmask is set to the default bitmask
// that would be used if compression was set to 0, we can continue as if compression was 0
if compression == 3 && infoLen > infoHeaderLen &&
readUint32(b[54:58]) == 0xff0000 && readUint32(b[58:62]) == 0xff00 &&
@@ -176,16 +187,16 @@ func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown b
compression = 0
}
if planes != 1 || compression != 0 {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
switch bpp {
case 8:
if offset != fileHeaderLen+infoLen+256*4 {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
_, err = io.ReadFull(r, b[:256*4])
if err != nil {
- return image.Config{}, 0, false, err
+ return image.Config{}, 0, false, false, err
}
pcm := make(color.Palette, 256)
for i := range pcm {
@@ -193,19 +204,40 @@ func decodeConfig(r io.Reader) (config image.Config, bitsPerPixel int, topDown b
// Every 4th byte is padding.
pcm[i] = color.RGBA{b[4*i+2], b[4*i+1], b[4*i+0], 0xFF}
}
- return image.Config{ColorModel: pcm, Width: width, Height: height}, 8, topDown, nil
+ return image.Config{ColorModel: pcm, Width: width, Height: height}, 8, topDown, false, nil
case 24:
if offset != fileHeaderLen+infoLen {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
- return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 24, topDown, nil
+ return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 24, topDown, false, nil
case 32:
if offset != fileHeaderLen+infoLen {
- return image.Config{}, 0, false, ErrUnsupported
+ return image.Config{}, 0, false, false, ErrUnsupported
}
- return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 32, topDown, nil
- }
- return image.Config{}, 0, false, ErrUnsupported
+ // 32 bits per pixel is possibly RGBX (X is padding) or RGBA (A is
+ // alpha transparency). However, for BMP images, "Alpha is a
+ // poorly-documented and inconsistently-used feature" says
+ // https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.cc;l=621
+ //
+ // That goes on to say "BITMAPV3HEADER+ have an alpha bitmask in the
+ // info header... so we respect it at all times... [For earlier
+ // (smaller) headers we] ignore alpha in Windows V3 BMPs except inside
+ // ICO files".
+ //
+ // "Ignore" means to always set alpha to 0xFF (fully opaque):
+ // https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.h;l=272
+ //
+ // Confusingly, "Windows V3" does not correspond to BITMAPV3HEADER, but
+ // instead corresponds to the earlier (smaller) BITMAPINFOHEADER:
+ // https://source.chromium.org/chromium/chromium/src/+/bc0a792d7ebc587190d1a62ccddba10abeea274b:third_party/blink/renderer/platform/image-decoders/bmp/bmp_image_reader.cc;l=258
+ //
+ // This Go package does not support ICO files and the (infoLen >
+ // infoHeaderLen) condition distinguishes BITMAPINFOHEADER (40 bytes)
+ // vs later (larger) headers.
+ allowAlpha = infoLen > infoHeaderLen
+ return image.Config{ColorModel: color.RGBAModel, Width: width, Height: height}, 32, topDown, allowAlpha, nil
+ }
+ return image.Config{}, 0, false, false, ErrUnsupported
}
func init() {
generated by cgit v1.2.3 (git 2.46.0) at 2025-07-13 02:33:48 +0000