Function newBitmap

bitmap.go:78–118

newBitmap creates a bitmap with given size in native pixels and DPI.

(size Size, transparent bool, dpi int)

// newBitmap creates a bitmap with given size in native pixels and DPI.
func newBitmap(size Size, transparent bool, dpi int) (bmp *Bitmap, err error) {
	err = withCompatibleDC(func(hdc win.HDC) error {
		bufSize := int(size.Width * size.Height * 4)

		var hdr win.BITMAPINFOHEADER
		hdr.BiSize = uint32(unsafe.Sizeof(hdr))
		hdr.BiBitCount = 32
		hdr.BiCompression = win.BI_RGB
		hdr.BiPlanes = 1
		hdr.BiWidth = int32(size.Width)
		hdr.BiHeight = int32(size.Height)
		hdr.BiSizeImage = uint32(bufSize)
		dpm := int32(math.Round(float64(dpi) * inchesPerMeter))
		hdr.BiXPelsPerMeter = dpm
		hdr.BiYPelsPerMeter = dpm

		var bitsPtr unsafe.Pointer

		hBmp := win.CreateDIBSection(hdc, &hdr, win.DIB_RGB_COLORS, &bitsPtr, 0, 0)
		switch hBmp {
		case 0, win.ERROR_INVALID_PARAMETER:
			return newError("CreateDIBSection failed")
		}

		if transparent {
			win.GdiFlush()

			bits := (*[1 << 24]byte)(bitsPtr)

			for i := 0; i < bufSize; i += 4 {
				// Mark pixel as not drawn to by GDI.
				bits[i+3] = 0x01
			}
		}

		bmp, err = newBitmapFromHBITMAP(hBmp, dpi)
		return err
	})

	return
}

// NewBitmapFromFile creates new bitmap from a bitmap file at 96dpi.
//