Start work on image support for new diff kitten

tools/cmd/icat/native.go

@@ -136,18 +136,7 @@ func calc_min_gap(gaps []int) int {
 }
 
 func (frame *image_frame) set_disposal(anchor_frame int, disposal byte) int {
-	if frame.number > 1 {
+	anchor_frame, frame.compose_onto = images.SetGIFFrameDisposal(frame.number, anchor_frame, disposal)
-		switch disposal {
-		case gif.DisposalNone:
-			frame.compose_onto = frame.number - 1
-			anchor_frame = frame.number
-		case gif.DisposalBackground:
-			// see https://github.com/golang/go/issues/20694
-			anchor_frame = frame.number
-		case gif.DisposalPrevious:
-			frame.compose_onto = anchor_frame
-		}
-	}
 	return anchor_frame
 }
 
@@ -159,7 +148,7 @@ func (frame *image_frame) set_delay(gap, min_gap int) {
 }
 
 func add_gif_frames(ctx *images.Context, imgd *image_data, gf *gif.GIF) error {
-	min_gap := calc_min_gap(gf.Delay)
+	min_gap := images.CalcMinimumGIFGap(gf.Delay)
 	scale_image(imgd)
 	anchor_frame := 1
 	for i, paletted_img := range gf.Image {

tools/utils/images/loading.go

@@ -0,0 +1,133 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package images
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"image/gif"
+	"io"
+	"os"
+	"strings"
+
+	"kitty/tools/utils"
+
+	"github.com/disintegration/imaging"
+)
+
+var _ = fmt.Print
+
+type ImageFrame struct {
+	Width, Height, Left, Top int
+	Number                   int   // 1-based number
+	Compose_onto             int   // number of frame to compose onto
+	Delay_ms                 int32 // negative for gapless frame, zero ignored, positive is number of ms
+	Is_opaque                bool
+	Img                      image.Image
+}
+
+type ImageData struct {
+	Width, Height    int
+	Format_uppercase string
+	Frames           []*ImageFrame
+}
+
+func CalcMinimumGIFGap(gaps []int) int {
+	// Some broken GIF images have all zero gaps, browsers with their usual
+	// idiot ideas render these with a default 100ms gap https://bugzilla.mozilla.org/show_bug.cgi?id=125137
+	// Browsers actually force a 100ms gap at any zero gap frame, but that
+	// just means it is impossible to deliberately use zero gap frames for
+	// sophisticated blending, so we dont do that.
+	max_gap := utils.Max(0, gaps...)
+	min_gap := 0
+	if max_gap <= 0 {
+		min_gap = 10
+	}
+	return min_gap
+}
+
+func SetGIFFrameDisposal(number, anchor_frame int, disposal byte) (int, int) {
+	compose_onto := 0
+	if number > 1 {
+		switch disposal {
+		case gif.DisposalNone:
+			compose_onto = number - 1
+			anchor_frame = number
+		case gif.DisposalBackground:
+			// see https://github.com/golang/go/issues/20694
+			anchor_frame = number
+		case gif.DisposalPrevious:
+			compose_onto = anchor_frame
+		}
+	}
+	return anchor_frame, compose_onto
+}
+
+func open_native_gif(f io.Reader, ans *ImageData) error {
+	gif_frames, err := gif.DecodeAll(f)
+	if err != nil {
+		return err
+	}
+	min_gap := CalcMinimumGIFGap(gif_frames.Delay)
+	anchor_frame := 1
+	for i, paletted_img := range gif_frames.Image {
+		b := paletted_img.Bounds()
+		frame := ImageFrame{Img: paletted_img, Left: b.Min.X, Top: b.Min.Y, Width: b.Dx(), Height: b.Dy(), Number: len(ans.Frames) + 1, Is_opaque: paletted_img.Opaque()}
+		frame.Delay_ms = int32(utils.Max(min_gap, gif_frames.Delay[i]) * 10)
+		if frame.Delay_ms == 0 {
+			frame.Delay_ms = -1 // gapless frame
+		}
+		anchor_frame, frame.Compose_onto = SetGIFFrameDisposal(frame.Number, anchor_frame, gif_frames.Disposal[i])
+		ans.Frames = append(ans.Frames, &frame)
+	}
+	return nil
+}
+
+func OpenNativeImageFromReader(f io.ReadSeeker) (ans *ImageData, err error) {
+	c, fmt, err := image.DecodeConfig(f)
+	if err != nil {
+		return nil, err
+	}
+	f.Seek(0, os.SEEK_SET)
+	ans = &ImageData{Width: c.Width, Height: c.Height, Format_uppercase: strings.ToUpper(fmt)}
+
+	if ans.Format_uppercase == "GIF" {
+		err = open_native_gif(f, ans)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		img, err := imaging.Decode(f, imaging.AutoOrientation(true))
+		if err != nil {
+			return nil, err
+		}
+		b := img.Bounds()
+		ans.Frames = []*ImageFrame{{Img: img, Left: b.Min.X, Top: b.Min.Y, Width: b.Dx(), Height: b.Dy()}}
+		ans.Frames[0].Is_opaque = c.ColorModel == color.YCbCrModel || c.ColorModel == color.GrayModel || c.ColorModel == color.Gray16Model || c.ColorModel == color.CMYKModel || ans.Format_uppercase == "JPEG" || ans.Format_uppercase == "JPG" || IsOpaque(img)
+	}
+	return
+}
+
+func OpenMagickImageFromPath(path string) (ans *ImageData, err error) {
+	// TODO: Implement this
+	return
+}
+
+func OpenImageFromPath(path string) (ans *ImageData, err error) {
+	mt := utils.GuessMimeType(path)
+	if DecodableImageTypes[mt] {
+		f, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		defer f.Close()
+		ans, err = OpenNativeImageFromReader(f)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to load image at %#v with error: %w", path, err)
+		}
+	} else {
+		return OpenMagickImageFromPath(path)
+	}
+	return
+}