func()

in tiff/reader.go [212:397]
180 lines of code
48 McCabe index (conditional complexity)

func (d *decoder) decode(dst image.Image, xmin, ymin, xmax, ymax int) error {
	d.off = 0

	// Apply horizontal predictor if necessary.
	// In this case, p contains the color difference to the preceding pixel.
	// See page 64-65 of the spec.
	if d.firstVal(tPredictor) == prHorizontal {
		switch d.bpp {
		case 16:
			var off int
			n := 2 * len(d.features[tBitsPerSample]) // bytes per sample times samples per pixel
			for y := ymin; y < ymax; y++ {
				off += n
				for x := 0; x < (xmax-xmin-1)*n; x += 2 {
					if off+2 > len(d.buf) {
						return errNoPixels
					}
					v0 := d.byteOrder.Uint16(d.buf[off-n : off-n+2])
					v1 := d.byteOrder.Uint16(d.buf[off : off+2])
					d.byteOrder.PutUint16(d.buf[off:off+2], v1+v0)
					off += 2
				}
			}
		case 8:
			var off int
			n := 1 * len(d.features[tBitsPerSample]) // bytes per sample times samples per pixel
			for y := ymin; y < ymax; y++ {
				off += n
				for x := 0; x < (xmax-xmin-1)*n; x++ {
					if off >= len(d.buf) {
						return errNoPixels
					}
					d.buf[off] += d.buf[off-n]
					off++
				}
			}
		case 1:
			return UnsupportedError("horizontal predictor with 1 BitsPerSample")
		}
	}

	rMaxX := minInt(xmax, dst.Bounds().Max.X)
	rMaxY := minInt(ymax, dst.Bounds().Max.Y)
	switch d.mode {
	case mGray, mGrayInvert:
		if d.bpp == 16 {
			img := dst.(*image.Gray16)
			for y := ymin; y < rMaxY; y++ {
				for x := xmin; x < rMaxX; x++ {
					if d.off+2 > len(d.buf) {
						return errNoPixels
					}
					v := d.byteOrder.Uint16(d.buf[d.off : d.off+2])
					d.off += 2
					if d.mode == mGrayInvert {
						v = 0xffff - v
					}
					img.SetGray16(x, y, color.Gray16{v})
				}
				if rMaxX == img.Bounds().Max.X {
					d.off += 2 * (xmax - img.Bounds().Max.X)
				}
			}
		} else {
			img := dst.(*image.Gray)
			max := uint32((1 << d.bpp) - 1)
			for y := ymin; y < rMaxY; y++ {
				for x := xmin; x < rMaxX; x++ {
					v, ok := d.readBits(d.bpp)
					if !ok {
						return errNoPixels
					}
					v = v * 0xff / max
					if d.mode == mGrayInvert {
						v = 0xff - v
					}
					img.SetGray(x, y, color.Gray{uint8(v)})
				}
				d.flushBits()
			}
		}
	case mPaletted:
		img := dst.(*image.Paletted)
		for y := ymin; y < rMaxY; y++ {
			for x := xmin; x < rMaxX; x++ {
				v, ok := d.readBits(d.bpp)
				if !ok {
					return errNoPixels
				}
				img.SetColorIndex(x, y, uint8(v))
			}
			d.flushBits()
		}
	case mRGB:
		if d.bpp == 16 {
			img := dst.(*image.RGBA64)
			for y := ymin; y < rMaxY; y++ {
				for x := xmin; x < rMaxX; x++ {
					if d.off+6 > len(d.buf) {
						return errNoPixels
					}
					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
					d.off += 6
					img.SetRGBA64(x, y, color.RGBA64{r, g, b, 0xffff})
				}
			}
		} else {
			img := dst.(*image.RGBA)
			for y := ymin; y < rMaxY; y++ {
				min := img.PixOffset(xmin, y)
				max := img.PixOffset(rMaxX, y)
				off := (y - ymin) * (xmax - xmin) * 3
				for i := min; i < max; i += 4 {
					if off+3 > len(d.buf) {
						return errNoPixels
					}
					img.Pix[i+0] = d.buf[off+0]
					img.Pix[i+1] = d.buf[off+1]
					img.Pix[i+2] = d.buf[off+2]
					img.Pix[i+3] = 0xff
					off += 3
				}
			}
		}
	case mNRGBA:
		if d.bpp == 16 {
			img := dst.(*image.NRGBA64)
			for y := ymin; y < rMaxY; y++ {
				for x := xmin; x < rMaxX; x++ {
					if d.off+8 > len(d.buf) {
						return errNoPixels
					}
					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
					a := d.byteOrder.Uint16(d.buf[d.off+6 : d.off+8])
					d.off += 8
					img.SetNRGBA64(x, y, color.NRGBA64{r, g, b, a})
				}
			}
		} else {
			img := dst.(*image.NRGBA)
			for y := ymin; y < rMaxY; y++ {
				min := img.PixOffset(xmin, y)
				max := img.PixOffset(rMaxX, y)
				i0, i1 := (y-ymin)*(xmax-xmin)*4, (y-ymin+1)*(xmax-xmin)*4
				if i1 > len(d.buf) {
					return errNoPixels
				}
				copy(img.Pix[min:max], d.buf[i0:i1])
			}
		}
	case mRGBA:
		if d.bpp == 16 {
			img := dst.(*image.RGBA64)
			for y := ymin; y < rMaxY; y++ {
				for x := xmin; x < rMaxX; x++ {
					if d.off+8 > len(d.buf) {
						return errNoPixels
					}
					r := d.byteOrder.Uint16(d.buf[d.off+0 : d.off+2])
					g := d.byteOrder.Uint16(d.buf[d.off+2 : d.off+4])
					b := d.byteOrder.Uint16(d.buf[d.off+4 : d.off+6])
					a := d.byteOrder.Uint16(d.buf[d.off+6 : d.off+8])
					d.off += 8
					img.SetRGBA64(x, y, color.RGBA64{r, g, b, a})
				}
			}
		} else {
			img := dst.(*image.RGBA)
			for y := ymin; y < rMaxY; y++ {
				min := img.PixOffset(xmin, y)
				max := img.PixOffset(rMaxX, y)
				i0, i1 := (y-ymin)*(xmax-xmin)*4, (y-ymin+1)*(xmax-xmin)*4
				if i1 > len(d.buf) {
					return errNoPixels
				}
				copy(img.Pix[min:max], d.buf[i0:i1])
			}
		}
	}

	return nil
}