use scale flag for no-fit and customizing zoom

ci/release/template/man/d2.1

@@ -80,6 +80,9 @@ Renders the diagram to look like it was sketched by hand
 .It Fl -center Ar flag
 Center the SVG in the containing viewbox, such as your browser screen
 .Ns .
+.It Fl -scale Ar fit
+Set a fixed render scale (e.g. 0.5 to halve rendered size). If none provided, SVG will fit to screen
+.Ns .
 .It Fl -font-regular
 Path to .ttf file to use for the regular font. If none provided, Source Sans Pro Regular is used
 .Ns .

d2cli/main.go

@@ -107,6 +107,7 @@ func Run(ctx context.Context, ms *xmain.State) (err error) {
 	if err != nil {
 		return err
 	}
+	scaleFlag := ms.Opts.String("SCALE", "scale", "", "fit", "set a fixed render scale (e.g. 0.5 to halve rendered size). If none provided, SVG will fit to screen.")
 
 	fontRegularFlag := ms.Opts.String("D2_FONT_REGULAR", "font-regular", "", "", "path to .ttf file to use for the regular font. If none provided, Source Sans Pro Regular is used.")
 	fontItalicFlag := ms.Opts.String("D2_FONT_ITALIC", "font-italic", "", "", "path to .ttf file to use for the italic font. If none provided, Source Sans Pro Regular-Italic is used.")
@@ -232,6 +233,14 @@ func Run(ctx context.Context, ms *xmain.State) (err error) {
 		}
 		ms.Log.Debug.Printf("using dark theme %s (ID: %d)", match.Name, *darkThemeFlag)
 	}
+	var scale *float64
+	if scaleFlag != nil && *scaleFlag != "fit" {
+		f, err := strconv.ParseFloat(*scaleFlag, 64)
+		if err != nil || f <= 0. {
+			return xmain.UsageErrorf("-scale must a positive floating point number or \"fit\".")
+		}
+		scale = &f
+	}
 
 	plugin, err := d2plugin.FindPlugin(ctx, ps, *layoutFlag)
 	if err != nil {
@@ -282,6 +291,7 @@ func Run(ctx context.Context, ms *xmain.State) (err error) {
 		Center:      *centerFlag,
 		ThemeID:     *themeFlag,
 		DarkThemeID: darkThemeFlag,
+		Scale:       scale,
 	}
 
 	if *watchFlag {
@@ -665,14 +675,20 @@ func render(ctx context.Context, ms *xmain.State, compileDur time.Duration, plug
 
 func _render(ctx context.Context, ms *xmain.State, plugin d2plugin.Plugin, opts d2svg.RenderOpts, outputPath string, bundle, forceAppendix bool, page playwright.Page, ruler *textmeasure.Ruler, diagram *d2target.Diagram) ([]byte, error) {
 	toPNG := getExportExtension(outputPath) == PNG
+	var scale *float64
+	if opts.Scale != nil {
+		scale = opts.Scale
+	} else if toPNG {
+		scale = go2.Pointer(1.)
+	}
 	svg, err := d2svg.Render(diagram, &d2svg.RenderOpts{
-		Pad:           opts.Pad,
+		Pad:         opts.Pad,
-		Sketch:        opts.Sketch,
+		Sketch:      opts.Sketch,
-		Center:        opts.Center,
+		Center:      opts.Center,
-		ThemeID:       opts.ThemeID,
+		ThemeID:     opts.ThemeID,
-		DarkThemeID:   opts.DarkThemeID,
+		DarkThemeID: opts.DarkThemeID,
-		MasterID:      opts.MasterID,
+		MasterID:    opts.MasterID,
-		SetDimensions: toPNG,
+		Scale:       scale,
 	})
 	if err != nil {
 		return nil, err
@@ -746,11 +762,18 @@ func renderPDF(ctx context.Context, ms *xmain.State, plugin d2plugin.Plugin, opt
 		// make the bg fill within the png transparent so that the pdf bg fill is the only bg color present
 		diagram.Root.Fill = "transparent"
 
+		var scale *float64
+		if opts.Scale != nil {
+			scale = opts.Scale
+		} else {
+			scale = go2.Pointer(1.)
+		}
+
 		svg, err = d2svg.Render(diagram, &d2svg.RenderOpts{
-			Pad:           opts.Pad,
+			Pad:    opts.Pad,
-			Sketch:        opts.Sketch,
+			Sketch: opts.Sketch,
-			Center:        opts.Center,
+			Center: opts.Center,
-			SetDimensions: true,
+			Scale:  scale,
 		})
 		if err != nil {
 			return nil, err
@@ -837,12 +860,20 @@ func renderPPTX(ctx context.Context, ms *xmain.State, presentation *pptx.Present
 		// make the bg fill within the png transparent so that the pdf bg fill is the only bg color present
 		diagram.Root.Fill = "transparent"
 
+		var scale *float64
+		if opts.Scale != nil {
+			scale = opts.Scale
+		} else {
+			scale = go2.Pointer(1.)
+		}
+
 		var err error
+
 		svg, err = d2svg.Render(diagram, &d2svg.RenderOpts{
-			Pad:           opts.Pad,
+			Pad:    opts.Pad,
-			Sketch:        opts.Sketch,
+			Sketch: opts.Sketch,
-			Center:        opts.Center,
+			Center: opts.Center,
-			SetDimensions: true,
+			Scale:  scale,
 		})
 		if err != nil {
 			return nil, err
@@ -1076,11 +1107,18 @@ func buildBoardIDToIndex(diagram *d2target.Diagram, dictionary map[string]int, p
 
 func renderPNGsForGIF(ctx context.Context, ms *xmain.State, plugin d2plugin.Plugin, opts d2svg.RenderOpts, ruler *textmeasure.Ruler, page playwright.Page, diagram *d2target.Diagram) (svg []byte, pngs [][]byte, err error) {
 	if !diagram.IsFolderOnly {
+
+		var scale *float64
+		if opts.Scale != nil {
+			scale = opts.Scale
+		} else {
+			scale = go2.Pointer(1.)
+		}
 		svg, err = d2svg.Render(diagram, &d2svg.RenderOpts{
-			Pad:           opts.Pad,
+			Pad:    opts.Pad,
-			Sketch:        opts.Sketch,
+			Sketch: opts.Sketch,
-			Center:        opts.Center,
+			Center: opts.Center,
-			SetDimensions: true,
+			Scale:  scale,
 		})
 		if err != nil {
 			return nil, nil, err

d2cli/static/watch.js

@@ -35,12 +35,16 @@ function init(reconnectDelay) {
       let width = parseInt(svgEl.getAttribute("width"), 10);
       let height = parseInt(svgEl.getAttribute("height"), 10);
       if (isInit) {
-        if (width > height) {
+        if (msg.scale) {
-          if (width > window.innerWidth) {
+          ratio = msg.scale;
-            ratio = window.innerWidth / width;
+        } else {
+          if (width > height) {
+            if (width > window.innerWidth) {
+              ratio = window.innerWidth / width;
+            }
+          } else if (height > window.innerHeight) {
+            ratio = window.innerHeight / height;
           }
-        } else if (height > window.innerHeight) {
-          ratio = window.innerHeight / height;
         }
         // Scale svg fit to zoom
         isInit = false;

d2cli/watch.go

@@ -83,8 +83,9 @@ type watcher struct {
 }
 
 type compileResult struct {
-	SVG string `json:"svg"`
+	SVG   string   `json:"svg"`
-	Err string `json:"err"`
+	Scale *float64 `json:"scale,omitEmpty"`
+	Err   string   `json:"err"`
 }
 
 func newWatcher(ctx context.Context, ms *xmain.State, opts watcherOpts) (*watcher, error) {
@@ -372,8 +373,9 @@ func (w *watcher) compileLoop(ctx context.Context) error {
 			w.ms.Log.Error.Print(errs)
 		}
 		w.broadcast(&compileResult{
-			SVG: string(svg),
+			SVG:   string(svg),
-			Err: errs,
+			Scale: w.renderOpts.Scale,
+			Err:   errs,
 		})
 
 		if firstCompile {

d2renderers/d2svg/d2svg.go

@@ -75,8 +75,8 @@ type RenderOpts struct {
 	ThemeID     int64
 	DarkThemeID *int64
 	Font        string
-	// disables the fit to screen behavior and ensures the exported svg has the exact dimensions
+	// the svg will be scaled by this factor, if unset the svg will fit to screen
-	SetDimensions bool
+	Scale *float64
 
 	// MasterID is passed when the diagram should use something other than its own hash for unique targeting
 	// Currently, that's when multi-boards are collapsed
@@ -1648,7 +1648,7 @@ func Render(diagram *d2target.Diagram, opts *RenderOpts) ([]byte, error) {
 	pad := DEFAULT_PADDING
 	themeID := DEFAULT_THEME
 	darkThemeID := DEFAULT_DARK_THEME
-	setDimensions := false
+	var scale *float64
 	if opts != nil {
 		pad = opts.Pad
 		if opts.Sketch {
@@ -1660,7 +1660,7 @@ func Render(diagram *d2target.Diagram, opts *RenderOpts) ([]byte, error) {
 		}
 		themeID = opts.ThemeID
 		darkThemeID = opts.DarkThemeID
-		setDimensions = opts.SetDimensions
+		scale = opts.Scale
 	}
 
 	buf := &bytes.Buffer{}
@@ -1851,8 +1851,11 @@ func Render(diagram *d2target.Diagram, opts *RenderOpts) ([]byte, error) {
 	}
 
 	var dimensions string
-	if setDimensions {
+	if scale != nil {
-		dimensions = fmt.Sprintf(` width="%d" height="%d"`, w, h)
+		dimensions = fmt.Sprintf(` width="%d" height="%d"`,
+			int(math.Ceil((*scale)*float64(w))),
+			int(math.Ceil((*scale)*float64(h))),
+		)
 	}
 
 	alignment := "xMinYMin"