mirror of https://github.com/rivo/tview.git
Started implementation of Image widget.
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Oliver
parent
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commit
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package tview
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import (
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"image"
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"math"
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)
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// Types of dithering applied to images.
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const (
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ImageDitheringNone = iota // No dithering.
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ImageDitheringThreshold // Grey scale thresholding at 50%.
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ImageDitheringFloydSteinberg // Floyd-Steinberg dithering (the default).
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)
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// The number of colors supported by true color terminals (R*G*B = 256*256*256).
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const TrueColor = 16777216
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// Image implements a widget that displays one image. The original image
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// (specified with [SetImage]) is resized according to the widget's size (see
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// [SetSize]), using the colors available in the terminal (see [SetColors]),
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// applying dithering if necessary (see [SetDithering]).
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//
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// Images are approximated by graphical characters in the terminal. The
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// resolution is therefore limited by the number of characters that can be drawn
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// in the terminal and the colors available in the terminal.
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//
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// Don't rely on the exact pixels drawn by this widget. The image drawing
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// algorithm may change in the future to improve the appearance of the image.
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type Image struct {
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*Box
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// The image to be displayed. If nil, the widget will be empty.
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image image.Image
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// The size of the image. If a value is 0, the corresponding size is chosen
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// automatically based on the other size while preserving the image's aspect
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// ratio. If both are 0, the image uses as much space as possible. A
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// negative value represents a percentage, e.g. -50 means 50% of the
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// available space.
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width, height int
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// The number of colors to use. If 0, the number of colors is chosen based
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// on the terminal's capabilities.
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colors int
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// The dithering algorithm to use, one of the constants starting with
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// "ImageDithering".
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dithering int
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// The background color to use (RGB) for transparent pixels.
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backgroundColor [3]int8
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// The width of a terminal's cell divided by its height.
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aspectRatio float64
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// Horizontal and vertical alignment, one of the "Align" constants.
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alignHorizontal, alignVertical int
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// The actual image size (in cells) when it was drawn the last time.
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lastWidth, lastHeight int
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// The actual image (in cells) when it was drawn the last time. The size of
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// this slice is 4 * lastWidth * lastHeight (with a factor of 4 because we
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// can draw four pixels per cell), indexed by y*lastWidth*2 + x. Each pixel
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// is an RGB value (0-255).
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pixels [][3]int
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}
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// NewImage returns a new image widget with an empty image (use [SetImage] to
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// specify the image to be displayed). The image will use the widget's entire
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// available space. The dithering algorithm is set to Floyd-Steinberg dithering.
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// The terminal's cell aspect ratio is set to 1.
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func NewImage() *Image {
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return &Image{
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Box: NewBox(),
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dithering: ImageDitheringFloydSteinberg,
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aspectRatio: 1,
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alignHorizontal: AlignCenter,
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alignVertical: AlignCenter,
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}
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}
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// SetImage sets the image to be displayed. If nil, the widget will be empty.
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func (i *Image) SetImage(image image.Image) *Image {
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i.image = image
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i.lastWidth, i.lastHeight = 0, 0
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return i
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}
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// SetSize sets the size of the image. Positive values refer to cells in the
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// terminal. Negative values refer to a percentage of the available space (e.g.
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// -50 means 50%). A value of 0 means that the corresponding size is chosen
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// automatically based on the other size while preserving the image's aspect
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// ratio. If both are 0, the image uses as much space as possible while still
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// preserving the aspect ratio.
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func (i *Image) SetSize(rows, columns int) *Image {
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i.width = columns
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i.height = rows
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return i
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}
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// SetColors sets the number of colors to use. This should be the number of
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// colors supported by the terminal. If 0, the number of colors is chosen based
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// on the $TERM environment variable (which may or may not be reliable).
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//
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// Only the values 0, 2, 8, 256, and 16777216 ([TrueColor]) are supported. Other
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// values will be rounded up to the next supported value, to a maximum of
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// 16777216.
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//
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// The effect of using more colors than supported by the terminal is undefined.
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func (i *Image) SetColors(colors int) *Image {
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i.colors = colors
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i.lastWidth, i.lastHeight = 0, 0
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return i
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}
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// SetDithering sets the dithering algorithm to use, one of the constants
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// starting with "ImageDithering", for example [ImageDitheringFloydSteinberg].
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func (i *Image) SetDithering(dithering int) *Image {
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i.dithering = dithering
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i.lastWidth, i.lastHeight = 0, 0
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return i
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}
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// SetBackgroundColor sets the background color to use (RGB) for transparent
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// pixels in the original image. The default is black (0, 0, 0).
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func (i *Image) SetBackgroundColor(r, g, b int8) *Image {
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i.backgroundColor = [3]int8{r, g, b}
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i.lastWidth, i.lastHeight = 0, 0
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return i
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}
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// SetAspectRatio sets the width of a terminal's cell divided by its height.
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// You may change the default of 1 if your terminal uses a different aspect
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// ratio. This is used to calculate the size of the image if one of the sizes
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// is 0. The function will panic if the aspect ratio is 0 or less.
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func (i *Image) SetAspectRatio(aspectRatio float64) *Image {
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if aspectRatio <= 0 {
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panic("aspect ratio must be greater than 0")
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}
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i.aspectRatio = aspectRatio
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i.lastWidth, i.lastHeight = 0, 0
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return i
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}
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// SetAlign sets the vertical and horizontal alignment of the image within the
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// widget's space. The possible values are [AlignTop], [AlignCenter], and
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// [AlignBottom] for vertical alignment and [AlignLeft], [AlignCenter], and
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// [AlignRight] for horizontal alignment. The default is [AlignCenter] for both.
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func (i *Image) SetAlign(vertical, horizontal int) *Image {
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i.alignHorizontal = horizontal
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i.alignVertical = vertical
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return i
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}
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// render re-populates the [Image.pixels] slice besed on the current settings,
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// if [Image.lastWidth] and [Image.lastHeight] don't match the current image's
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// size. It also sets the new image size in these two variables.
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func (i *Image) render() {
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// If there is no image, there are no pixels.
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if i.image == nil {
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i.pixels = nil
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return
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}
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// Calculate the new (terminal-space) image size.
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bounds := i.image.Bounds()
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imageWidth, imageHeight := bounds.Dx(), bounds.Dy()
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if i.aspectRatio != 1.0 {
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imageWidth = int(float64(imageWidth) / i.aspectRatio)
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}
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width, height := i.width, i.height
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_, _, innerWidth, innerHeight := i.GetInnerRect()
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if width == 0 && height == 0 {
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// Use all available space.
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width, height = innerWidth, innerHeight
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if adjustedWidth := imageWidth * height / imageHeight; adjustedWidth < width {
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width = adjustedWidth
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} else {
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height = imageHeight * width / imageWidth
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}
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} else {
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// Turn percentages into absolute values.
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if width < 0 {
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width = innerWidth * -width / 100
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}
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if height < 0 {
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height = innerHeight * -height / 100
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}
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if width == 0 {
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// Adjust the width.
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width = imageWidth * height / imageHeight
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} else if height == 0 {
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// Adjust the height.
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height = imageHeight * width / imageWidth
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}
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}
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if width <= 0 || height <= 0 {
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i.pixels = nil
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return
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}
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// If nothing has changed, we're done.
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if i.lastWidth == width && i.lastHeight == height {
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return
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}
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i.lastWidth, i.lastHeight = width, height // This could still be larger than the available space but that's ok for now.
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// Generate the initial pixels by resizing the image.
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i.resize()
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}
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// resize resizes the image to the current size and stores the result in
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// [Image.pixels]. It is assumed that [Image.lastWidth] and [Image.lastHeight]
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// are positive values.
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func (i *Image) resize() {
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// Because most of the time, we will be downsizing the image, we don't even
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// attempt to do any fancy interpolation. For each target pixel, we
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// calculate a weighted average of the source pixels using their coverage
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// area.
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bounds := i.image.Bounds()
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srcWidth, srcHeight := bounds.Dx(), bounds.Dy()
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tgtWidth, tgtHeight := i.lastWidth*2, i.lastHeight*2
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coverageWidth, coverageHeight := float64(srcWidth)/float64(tgtWidth), float64(srcHeight)/float64(tgtHeight)
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i.pixels = make([][3]int, tgtWidth*tgtHeight)
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weights := make([]float64, tgtWidth*tgtHeight)
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for srcY := bounds.Min.Y; srcY < bounds.Max.Y; srcY++ {
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for srcX := bounds.Min.X; srcX < bounds.Max.X; srcX++ {
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r32, g32, b32, _ := i.image.At(srcX, srcY).RGBA()
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r, g, b := int(r32>>8), int(g32>>8), int(b32>>8)
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// Iterate over all target pixels. Outer loop is Y.
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startY := float64(srcY-bounds.Min.Y) * coverageHeight
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endY := startY + coverageHeight
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fromY, toY := int(startY), int(endY)
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for tgtY := fromY; tgtY <= toY && tgtY < tgtHeight; tgtY++ {
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coverageY := 1.0
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if tgtY == fromY {
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coverageY -= math.Mod(startY, 1.0)
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}
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if tgtY == toY {
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coverageY -= 1.0 - math.Mod(endY, 1.0)
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}
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// Inner loop is X.
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startX := float64(srcX-bounds.Min.X) * coverageWidth
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endX := startX + coverageWidth
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fromX, toX := int(startX), int(endX)
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for tgtX := fromX; tgtX <= toX && tgtX < tgtWidth; tgtX++ {
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coverageX := 1.0
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if tgtX == fromX {
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coverageX -= math.Mod(startX, 1.0)
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}
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if tgtX == toX {
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coverageX -= 1.0 - math.Mod(endX, 1.0)
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}
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// Add a weighted contribution to the target pixel.
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index := tgtY*tgtWidth + tgtX
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i.pixels[index][0] += r
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i.pixels[index][1] += g
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i.pixels[index][2] += b
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weights[index] += coverageX * coverageY
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}
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}
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}
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}
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// Normalize the pixels.
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for index, weight := range weights {
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if weight > 0 {
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i.pixels[index][0] = int(float64(i.pixels[index][0]) / weight)
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i.pixels[index][1] = int(float64(i.pixels[index][1]) / weight)
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i.pixels[index][2] = int(float64(i.pixels[index][2]) / weight)
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}
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}
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}
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