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// Copyright 2024 The Forgejo Authors. All rights reserved.
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// Copyright 2025 The Tangled Authors -- repurposed for Tangled use.
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// SPDX-License-Identifier: MIT
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"github.com/goki/freetype"
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"github.com/goki/freetype/truetype"
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"github.com/srwiley/oksvg"
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"github.com/srwiley/rasterx"
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"golang.org/x/image/draw"
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"golang.org/x/image/font"
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"tangled.org/core/appview/pages"
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_ "golang.org/x/image/webp" // for processing webp images
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var fontCache = sync.OnceValues(func() (*truetype.Font, error) {
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interVar, err := pages.Files.ReadFile("static/fonts/InterVariable.ttf")
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return truetype.Parse(interVar)
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// DefaultSize returns the default size for a card
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func DefaultSize() (int, int) {
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// NewCard creates a new card with the given dimensions in pixels
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func NewCard(width, height int) (*Card, error) {
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img := image.NewRGBA(image.Rect(0, 0, width, height))
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draw.Draw(img, img.Bounds(), image.NewUniform(color.White), image.Point{}, draw.Src)
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font, err := fontCache()
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// Split splits the card horizontally or vertically by a given percentage; the first card returned has the percentage
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// size, and the second card has the remainder. Both cards draw to a subsection of the same image buffer.
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func (c *Card) Split(vertical bool, percentage int) (*Card, *Card) {
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bounds := c.Img.Bounds()
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bounds = image.Rect(bounds.Min.X+c.Margin, bounds.Min.Y+c.Margin, bounds.Max.X-c.Margin, bounds.Max.Y-c.Margin)
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mid := (bounds.Dx() * percentage / 100) + bounds.Min.X
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subleft := c.Img.SubImage(image.Rect(bounds.Min.X, bounds.Min.Y, mid, bounds.Max.Y)).(*image.RGBA)
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subright := c.Img.SubImage(image.Rect(mid, bounds.Min.Y, bounds.Max.X, bounds.Max.Y)).(*image.RGBA)
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return &Card{Img: subleft, Font: c.Font, Width: subleft.Bounds().Dx(), Height: subleft.Bounds().Dy()},
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&Card{Img: subright, Font: c.Font, Width: subright.Bounds().Dx(), Height: subright.Bounds().Dy()}
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mid := (bounds.Dy() * percentage / 100) + bounds.Min.Y
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subtop := c.Img.SubImage(image.Rect(bounds.Min.X, bounds.Min.Y, bounds.Max.X, mid)).(*image.RGBA)
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subbottom := c.Img.SubImage(image.Rect(bounds.Min.X, mid, bounds.Max.X, bounds.Max.Y)).(*image.RGBA)
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return &Card{Img: subtop, Font: c.Font, Width: subtop.Bounds().Dx(), Height: subtop.Bounds().Dy()},
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&Card{Img: subbottom, Font: c.Font, Width: subbottom.Bounds().Dx(), Height: subbottom.Bounds().Dy()}
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// SetMargin sets the margins for the card
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func (c *Card) SetMargin(margin int) {
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// DrawText draws text within the card, respecting margins and alignment
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func (c *Card) DrawText(text string, textColor color.Color, sizePt float64, valign VAlign, halign HAlign) ([]string, error) {
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ft := freetype.NewContext()
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ft.SetFontSize(sizePt)
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ft.SetClip(c.Img.Bounds())
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ft.SetSrc(image.NewUniform(textColor))
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face := truetype.NewFace(c.Font, &truetype.Options{Size: sizePt, DPI: 72})
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fontHeight := ft.PointToFixed(sizePt).Ceil()
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bounds := c.Img.Bounds()
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bounds = image.Rect(bounds.Min.X+c.Margin, bounds.Min.Y+c.Margin, bounds.Max.X-c.Margin, bounds.Max.Y-c.Margin)
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boxWidth, boxHeight := bounds.Size().X, bounds.Size().Y
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// draw.Draw(c.Img, bounds, image.NewUniform(color.Gray{128}), image.Point{}, draw.Src) // Debug draw box
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// Try to apply wrapping to this text; we'll find the most text that will fit into one line, record that line, move
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// on. We precalculate each line before drawing so that we can support valign="middle" correctly which requires
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// knowing the total height, which is related to how many lines we'll have.
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lines := make([]string, 0)
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textWords := strings.Split(text, " ")
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if len(textWords) == 0 {
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// Ran out of words.
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if currentLine != "" {
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heightTotal += fontHeight
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lines = append(lines, currentLine)
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nextWord := textWords[0]
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proposedLine := currentLine
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if proposedLine != "" {
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proposedLine += " "
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proposedLine += nextWord
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proposedLineWidth := font.MeasureString(face, proposedLine)
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if proposedLineWidth.Ceil() > boxWidth {
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// no, proposed line is too big; we'll use the last "currentLine"
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heightTotal += fontHeight
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if currentLine != "" {
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lines = append(lines, currentLine)
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// leave nextWord in textWords and keep going
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// just nextWord by itself doesn't fit on a line; well, we can't skip it, but we'll consume it
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// regardless as a line by itself. It will be clipped by the drawing routine.
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lines = append(lines, nextWord)
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textWords = textWords[1:]
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// yes, it will fit
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currentLine = proposedLine
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textWords = textWords[1:]
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textY = boxHeight - heightTotal + fontHeight
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textY = ((boxHeight - heightTotal) / 2) + fontHeight
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for _, line := range lines {
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lineWidth := font.MeasureString(face, line)
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textX = boxWidth - lineWidth.Ceil()
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textX = (boxWidth - lineWidth.Ceil()) / 2
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pt := freetype.Pt(bounds.Min.X+textX, bounds.Min.Y+textY)
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_, err := ft.DrawString(line, pt)
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textY += fontHeight
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// DrawTextAt draws text at a specific position with the given alignment
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func (c *Card) DrawTextAt(text string, x, y int, textColor color.Color, sizePt float64, valign VAlign, halign HAlign) error {
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_, err := c.DrawTextAtWithWidth(text, x, y, textColor, sizePt, valign, halign)
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// DrawTextAtWithWidth draws text at a specific position and returns the text width
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func (c *Card) DrawTextAtWithWidth(text string, x, y int, textColor color.Color, sizePt float64, valign VAlign, halign HAlign) (int, error) {
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ft := freetype.NewContext()
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ft.SetFontSize(sizePt)
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ft.SetClip(c.Img.Bounds())
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ft.SetSrc(image.NewUniform(textColor))
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face := truetype.NewFace(c.Font, &truetype.Options{Size: sizePt, DPI: 72})
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fontHeight := ft.PointToFixed(sizePt).Ceil()
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lineWidth := font.MeasureString(face, text)
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textWidth := lineWidth.Ceil()
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// Adjust position based on alignment
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// x is already at the left position
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adjustedX = x - textWidth
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adjustedX = x - textWidth/2
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adjustedY = y + fontHeight
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adjustedY = y + fontHeight/2
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pt := freetype.Pt(adjustedX, adjustedY)
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_, err := ft.DrawString(text, pt)
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return textWidth, err
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// DrawBoldText draws bold text by rendering multiple times with slight offsets
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func (c *Card) DrawBoldText(text string, x, y int, textColor color.Color, sizePt float64, valign VAlign, halign HAlign) (int, error) {
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// Draw the text multiple times with slight offsets to create bold effect
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offsets := []struct{ dx, dy int }{
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{0, 0}, // original
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{1, 1}, // diagonal
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for _, offset := range offsets {
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w, err := c.DrawTextAtWithWidth(text, x+offset.dx, y+offset.dy, textColor, sizePt, valign, halign)
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// DrawSVGIcon draws an SVG icon from the embedded files at the specified position
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func (c *Card) DrawSVGIcon(svgPath string, x, y, size int, iconColor color.Color) error {
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svgData, err := pages.Files.ReadFile(svgPath)
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return fmt.Errorf("failed to read SVG file %s: %w", svgPath, err)
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// Convert color to hex string for SVG
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rgba, isRGBA := iconColor.(color.RGBA)
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r, g, b, a := iconColor.RGBA()
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rgba = color.RGBA{uint8(r >> 8), uint8(g >> 8), uint8(b >> 8), uint8(a >> 8)}
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colorHex := fmt.Sprintf("#%02x%02x%02x", rgba.R, rgba.G, rgba.B)
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// Replace currentColor with our desired color in the SVG
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svgString := string(svgData)
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svgString = strings.ReplaceAll(svgString, "currentColor", colorHex)
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// Make the stroke thicker
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svgString = strings.ReplaceAll(svgString, `stroke-width="2"`, `stroke-width="3"`)
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icon, err := oksvg.ReadIconStream(strings.NewReader(svgString))
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return fmt.Errorf("failed to parse SVG %s: %w", svgPath, err)
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// Set the icon size
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w, h := float64(size), float64(size)
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icon.SetTarget(0, 0, w, h)
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// Create a temporary RGBA image for the icon
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iconImg := image.NewRGBA(image.Rect(0, 0, size, size))
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// Create scanner and rasterizer
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scanner := rasterx.NewScannerGV(size, size, iconImg, iconImg.Bounds())
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raster := rasterx.NewDasher(size, size, scanner)
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icon.Draw(raster, 1.0)
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// Draw the icon onto the card at the specified position
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bounds := c.Img.Bounds()
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destRect := image.Rect(x, y, x+size, y+size)
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// Make sure we don't draw outside the card bounds
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if destRect.Max.X > bounds.Max.X {
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destRect.Max.X = bounds.Max.X
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if destRect.Max.Y > bounds.Max.Y {
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destRect.Max.Y = bounds.Max.Y
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draw.Draw(c.Img, destRect, iconImg, image.Point{}, draw.Over)
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// DrawImage fills the card with an image, scaled to maintain the original aspect ratio and centered with respect to the non-filled dimension
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func (c *Card) DrawImage(img image.Image) {
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bounds := c.Img.Bounds()
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targetRect := image.Rect(bounds.Min.X+c.Margin, bounds.Min.Y+c.Margin, bounds.Max.X-c.Margin, bounds.Max.Y-c.Margin)
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srcBounds := img.Bounds()
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srcAspect := float64(srcBounds.Dx()) / float64(srcBounds.Dy())
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targetAspect := float64(targetRect.Dx()) / float64(targetRect.Dy())
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if srcAspect > targetAspect {
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// Image is wider than target, scale by width
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scale = float64(targetRect.Dx()) / float64(srcBounds.Dx())
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// Image is taller or equal, scale by height
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scale = float64(targetRect.Dy()) / float64(srcBounds.Dy())
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newWidth := int(math.Round(float64(srcBounds.Dx()) * scale))
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newHeight := int(math.Round(float64(srcBounds.Dy()) * scale))
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// Center the image within the target rectangle
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offsetX := (targetRect.Dx() - newWidth) / 2
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offsetY := (targetRect.Dy() - newHeight) / 2
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scaledRect := image.Rect(targetRect.Min.X+offsetX, targetRect.Min.Y+offsetY, targetRect.Min.X+offsetX+newWidth, targetRect.Min.Y+offsetY+newHeight)
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draw.CatmullRom.Scale(c.Img, scaledRect, img, srcBounds, draw.Over, nil)
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func fallbackImage() image.Image {
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// can't usage image.Uniform(color.White) because it's infinitely sized causing a panic in the scaler in DrawImage
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img := image.NewRGBA(image.Rect(0, 0, 1, 1))
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img.Set(0, 0, color.White)
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// As defensively as possible, attempt to load an image from a presumed external and untrusted URL
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func (c *Card) fetchExternalImage(url string) (image.Image, bool) {
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// Use a short timeout; in the event of any failure we'll be logging and returning a placeholder, but we don't want
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// this rendering process to be slowed down
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client := &http.Client{
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Timeout: 1 * time.Second, // 1 second timeout
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resp, err := client.Get(url)
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log.Printf("error when fetching external image from %s: %v", url, err)
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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log.Printf("non-OK error code when fetching external image from %s: %s", url, resp.Status)
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contentType := resp.Header.Get("Content-Type")
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// Support content types are in-sync with the allowed custom avatar file types
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if contentType != "image/png" && contentType != "image/jpeg" && contentType != "image/gif" && contentType != "image/webp" {
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log.Printf("fetching external image returned unsupported Content-Type which was ignored: %s", contentType)
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bodyBytes, err := io.ReadAll(body)
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log.Printf("error when fetching external image from %s: %v", url, err)
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bodyBuffer := bytes.NewReader(bodyBytes)
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_, imgType, err := image.DecodeConfig(bodyBuffer)
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log.Printf("error when decoding external image from %s: %v", url, err)
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// Verify that we have a match between actual data understood in the image body and the reported Content-Type
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if (contentType == "image/png" && imgType != "png") ||
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(contentType == "image/jpeg" && imgType != "jpeg") ||
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(contentType == "image/gif" && imgType != "gif") ||
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(contentType == "image/webp" && imgType != "webp") {
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log.Printf("while fetching external image, mismatched image body (%s) and Content-Type (%s)", imgType, contentType)
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_, err = bodyBuffer.Seek(0, io.SeekStart) // reset for actual decode
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log.Printf("error w/ bodyBuffer.Seek")
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img, _, err := image.Decode(bodyBuffer)
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log.Printf("error when decoding external image from %s: %v", url, err)
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func (c *Card) DrawExternalImage(url string) {
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image, ok := c.fetchExternalImage(url)
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image = fallbackImage()
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// DrawCircularExternalImage draws an external image as a circle at the specified position
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func (c *Card) DrawCircularExternalImage(url string, x, y, size int) error {
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img, ok := c.fetchExternalImage(url)
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img = fallbackImage()
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// Create a circular mask
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circle := image.NewRGBA(image.Rect(0, 0, size, size))
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radius := float64(size / 2)
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// Scale the source image to fit the circle
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srcBounds := img.Bounds()
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scaledImg := image.NewRGBA(image.Rect(0, 0, size, size))
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draw.CatmullRom.Scale(scaledImg, scaledImg.Bounds(), img, srcBounds, draw.Src, nil)
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// Draw the image with circular clipping
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for cy := 0; cy < size; cy++ {
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for cx := 0; cx < size; cx++ {
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// Calculate distance from center
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dx := float64(cx - center)
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dy := float64(cy - center)
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distance := math.Sqrt(dx*dx + dy*dy)
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// Only draw pixels within the circle
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if distance <= radius {
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circle.Set(cx, cy, scaledImg.At(cx, cy))
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// Draw the circle onto the card
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bounds := c.Img.Bounds()
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destRect := image.Rect(x, y, x+size, y+size)
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// Make sure we don't draw outside the card bounds
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if destRect.Max.X > bounds.Max.X {
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destRect.Max.X = bounds.Max.X
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if destRect.Max.Y > bounds.Max.Y {
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destRect.Max.Y = bounds.Max.Y
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draw.Draw(c.Img, destRect, circle, image.Point{}, draw.Over)
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// DrawRect draws a rect with the given color
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func (c *Card) DrawRect(startX, startY, endX, endY int, color color.Color) {
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draw.Draw(c.Img, image.Rect(startX, startY, endX, endY), &image.Uniform{color}, image.Point{}, draw.Src)
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