add test

e2etests-cli/main_test.go

@@ -10,6 +10,7 @@ import (
 
 	"oss.terrastruct.com/d2/d2cli"
 	"oss.terrastruct.com/d2/lib/pptx"
+	"oss.terrastruct.com/d2/lib/xgif"
 	"oss.terrastruct.com/util-go/assert"
 	"oss.terrastruct.com/util-go/diff"
 	"oss.terrastruct.com/util-go/xmain"
@@ -141,7 +142,7 @@ a -> b: italic font
 			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {
 				writeFile(t, dir, "x.d2", `x -> y`)
 				err := runTestMain(t, ctx, dir, env, "--animate-interval=2", "x.d2", "x.png")
-				assert.ErrorString(t, err, `failed to wait xmain test: e2etests-cli/d2: bad usage: -animate-interval can only be used when exporting to SVG.
+				assert.ErrorString(t, err, `failed to wait xmain test: e2etests-cli/d2: bad usage: -animate-interval can only be used when exporting to SVG or GIF.
 You provided: .png`)
 			},
 		},
@@ -277,6 +278,38 @@ steps: {
 				assert.Success(t, err)
 			},
 		},
+		{
+			name:   "how_to_solve_problems_gif",
+			skipCI: true,
+			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {
+				writeFile(t, dir, "in.d2", `how to solve a hard problem? {
+	link: steps.2
+}
+steps: {
+	1: {
+		w: write down the problem
+	}
+	2: {
+		w -> t
+		t: think really hard about it
+	}
+	3: {
+		t -> w2
+		w2: write down the solution
+		w2: {
+			link: https://d2lang.com
+		}
+	}
+}
+`)
+				err := runTestMain(t, ctx, dir, env, "--animate-interval=10", "in.d2", "how_to_solve_problems.gif")
+				assert.Success(t, err)
+
+				gifBytes := readFile(t, dir, "how_to_solve_problems.gif")
+				err = xgif.Validate(gifBytes, 4, 10)
+				assert.Success(t, err)
+			},
+		},
 		{
 			name: "stdin",
 			run: func(t *testing.T, ctx context.Context, dir string, env *xos.Env) {

lib/xgif/xgif.go

@@ -89,3 +89,36 @@ func AnimatePNGs(pngs [][]byte, animIntervalMs int) ([]byte, error) {
 	}
 	return buf.Bytes(), nil
 }
+
+func Validate(gifBytes []byte, nFrames int, intervalMS int) error {
+	anim, err := gif.DecodeAll(bytes.NewBuffer(gifBytes))
+	if err != nil {
+		return err
+	}
+
+	if anim.LoopCount != INFINITE_LOOP {
+		return fmt.Errorf("expected infinite loop, got=%d", anim.LoopCount)
+	}
+
+	if len(anim.Image) != nFrames {
+		return fmt.Errorf("expected %d frames, got=%d", nFrames, len(anim.Image))
+	}
+
+	interval := intervalMS / 10
+	width, height := anim.Config.Width, anim.Config.Height
+	for i, frame := range anim.Image {
+		w := frame.Bounds().Dx()
+		if w != width {
+			return fmt.Errorf("expected all frames to have the same width=%d, got=%d at frame=%d", width, w, i)
+		}
+		h := frame.Bounds().Dy()
+		if h != height {
+			return fmt.Errorf("expected all frames to have the same height=%d, got=%d at frame=%d", height, h, i)
+		}
+		if anim.Delay[i] != interval {
+			return fmt.Errorf("expected interval between frames to be %d, got=%d at frame=%d", interval, anim.Delay[i], i)
+		}
+	}
+
+	return nil
+}