Extract renderer-agnostic flamegraph layout

3 files changed, 160 insertions, 35 deletions

diff --git a/internal/flamegraph/layout.go b/internal/flamegraph/layout.go
new file mode 100644
index 0000000..c319800
--- /dev/null
+++ b/internal/flamegraph/layout.go
@@ -0,0 +1,78 @@
+package flamegraph
+
+import "fmt"
+
+// FrameLayout captures renderer-agnostic flamegraph geometry for a single frame.
+//
+// The layout is reusable by non-SVG renderers (for example SDL or WASM UIs) so
+// they can render the same hierarchy without depending on SVG internals.
+type FrameLayout struct {
+	Name    string
+	Title   string
+	Fill    string
+	X       float64
+	Y       float64
+	Width   float64
+	Height  float64
+	Depth   int
+	Total   uint64
+	Percent float64
+}
+
+func sanitizeSVGConfig(cfg SVGConfig) SVGConfig {
+	if cfg.Width <= 0 || cfg.FrameHeight <= 0 || cfg.FontSize <= 0 || cfg.MinWidthPx <= 0 {
+		return defaultSVGConfig()
+	}
+	if cfg.Title == "" {
+		cfg.Title = defaultSVGConfig().Title
+	}
+	return cfg
+}
+
+func canvasHeightFor(cfg SVGConfig, t *trie) int {
+	return cfg.FrameHeight*(t.maxDepth+1) + 80
+}
+
+// BuildFrameLayout builds renderer-agnostic frame coordinates from a flamegraph trie.
+func BuildFrameLayout(t *trie, cfg SVGConfig) []FrameLayout {
+	if t == nil || t.root == nil || t.root.total == 0 {
+		return nil
+	}
+	cfg = sanitizeSVGConfig(cfg)
+	canvasHeight := canvasHeightFor(cfg, t)
+	out := make([]FrameLayout, 0, len(t.root.children))
+	collectFrameLayout(&out, t.root, t.root.total, cfg, 0, 0, canvasHeight, true)
+	return out
+}
+
+func collectFrameLayout(out *[]FrameLayout, node *trieNode, rootTotal uint64,
+	cfg SVGConfig, x float64, depth int, canvasHeight int, isRoot bool) {
+
+	if !isRoot {
+		w := float64(cfg.Width) * (float64(node.total) / float64(rootTotal))
+		if w < cfg.MinWidthPx {
+			return
+		}
+		y := float64(canvasHeight - (depth+1)*cfg.FrameHeight)
+		pct := 100 * float64(node.total) / float64(rootTotal)
+		*out = append(*out, FrameLayout{
+			Name:    node.name,
+			Title:   fmt.Sprintf("%s (%d, %.2f%%)", node.name, node.total, pct),
+			Fill:    frameColor(node.name),
+			X:       x,
+			Y:       y,
+			Width:   w,
+			Height:  float64(cfg.FrameHeight - 1),
+			Depth:   depth,
+			Total:   node.total,
+			Percent: pct,
+		})
+	}
+
+	cursor := x
+	for _, child := range node.children {
+		cw := float64(cfg.Width) * (float64(child.total) / float64(rootTotal))
+		collectFrameLayout(out, child, rootTotal, cfg, cursor, depth+1, canvasHeight, false)
+		cursor += cw
+	}
+}
diff --git a/internal/flamegraph/layout_test.go b/internal/flamegraph/layout_test.go
new file mode 100644
index 0000000..8fa7398
--- /dev/null
+++ b/internal/flamegraph/layout_test.go
@@ -0,0 +1,77 @@
+package flamegraph
+
+import (
+	"math"
+	"testing"
+)
+
+func almostEqual(a, b float64) bool {
+	return math.Abs(a-b) < 1e-6
+}
+
+func TestBuildFrameLayoutBasicGeometry(t *testing.T) {
+	tr := newTrie()
+	tr.add([]string{"A"}, 4)
+	tr.add([]string{"B"}, 1)
+	tr.computeTotals()
+
+	cfg := defaultSVGConfig()
+	cfg.Width = 100
+	cfg.FrameHeight = 10
+	cfg.FontSize = 10
+	cfg.MinWidthPx = 1
+
+	frames := BuildFrameLayout(tr, cfg)
+	if len(frames) != 2 {
+		t.Fatalf("frames len = %d, want 2", len(frames))
+	}
+
+	a := frames[0]
+	if a.Name != "A" {
+		t.Fatalf("first frame name = %q, want %q", a.Name, "A")
+	}
+	if !almostEqual(a.X, 0) {
+		t.Fatalf("A x = %f, want 0", a.X)
+	}
+	if !almostEqual(a.Width, 80) {
+		t.Fatalf("A width = %f, want 80", a.Width)
+	}
+	if !almostEqual(a.Percent, 80) {
+		t.Fatalf("A percent = %f, want 80", a.Percent)
+	}
+	if a.Depth != 1 {
+		t.Fatalf("A depth = %d, want 1", a.Depth)
+	}
+
+	b := frames[1]
+	if b.Name != "B" {
+		t.Fatalf("second frame name = %q, want %q", b.Name, "B")
+	}
+	if !almostEqual(b.X, 80) {
+		t.Fatalf("B x = %f, want 80", b.X)
+	}
+	if !almostEqual(b.Width, 20) {
+		t.Fatalf("B width = %f, want 20", b.Width)
+	}
+}
+
+func TestBuildFrameLayoutSkipsFramesBelowMinWidth(t *testing.T) {
+	tr := newTrie()
+	tr.add([]string{"A"}, 999)
+	tr.add([]string{"B"}, 1)
+	tr.computeTotals()
+
+	cfg := defaultSVGConfig()
+	cfg.Width = 100
+	cfg.FrameHeight = 10
+	cfg.FontSize = 10
+	cfg.MinWidthPx = 1
+
+	frames := BuildFrameLayout(tr, cfg)
+	if len(frames) != 1 {
+		t.Fatalf("frames len = %d, want 1", len(frames))
+	}
+	if frames[0].Name != "A" {
+		t.Fatalf("remaining frame name = %q, want %q", frames[0].Name, "A")
+	}
+}
diff --git a/internal/flamegraph/svgwriter.go b/internal/flamegraph/svgwriter.go
index f8b70b3..7fd699e 100644
--- a/internal/flamegraph/svgwriter.go
+++ b/internal/flamegraph/svgwriter.go
@@ -58,20 +58,16 @@ func DefaultSVGConfig() SVGConfig {
 // for zoom, search, and highlighting, and is designed to be served directly to
 // a browser (for example via ServeSVG) without any external assets.
 func WriteSVG(w io.Writer, t *trie, cfg SVGConfig) error {
-	if cfg.Width <= 0 || cfg.FrameHeight <= 0 || cfg.FontSize <= 0 || cfg.MinWidthPx <= 0 {
-		cfg = defaultSVGConfig()
-	}
-	if cfg.Title == "" {
-		cfg.Title = defaultSVGConfig().Title
-	}
+	cfg = sanitizeSVGConfig(cfg)
 
-	canvasHeight := cfg.FrameHeight*(t.maxDepth+1) + 80
+	canvasHeight := canvasHeightFor(cfg, t)
 	bw := bufio.NewWriter(w)
 	if err := writeSVGHeader(bw, cfg, canvasHeight); err != nil {
 		return err
 	}
-	if t.root.total > 0 {
-		if err := renderFrames(bw, t.root, t.root.total, cfg, 0, 0, canvasHeight, true); err != nil {
+	for _, frame := range BuildFrameLayout(t, cfg) {
+		if err := writeFrame(bw, frame.Name, frame.Title, frame.Fill,
+			frame.X, frame.Y, frame.Width, frame.Height, frame.Depth, cfg.FontSize); err != nil {
 			return err
 		}
 	}
@@ -108,32 +104,6 @@ func writeSVGFooter(bw *bufio.Writer) error {
 	return err
 }
 
-func renderFrames(bw *bufio.Writer, node *trieNode, rootTotal uint64, cfg SVGConfig, x float64, depth int, canvasHeight int, isRoot bool) error {
-	if !isRoot {
-		w := float64(cfg.Width) * (float64(node.total) / float64(rootTotal))
-		if w < cfg.MinWidthPx {
-			return nil
-		}
-		y := float64(canvasHeight - (depth+1)*cfg.FrameHeight)
-		fill := frameColor(node.name)
-		pct := 100 * float64(node.total) / float64(rootTotal)
-		title := fmt.Sprintf("%s (%d, %.2f%%)", node.name, node.total, pct)
-		if err := writeFrame(bw, node.name, title, fill, x, y, w, float64(cfg.FrameHeight-1), depth, cfg.FontSize); err != nil {
-			return err
-		}
-	}
-
-	cursor := x
-	for _, child := range node.children {
-		cw := float64(cfg.Width) * (float64(child.total) / float64(rootTotal))
-		if err := renderFrames(bw, child, rootTotal, cfg, cursor, depth+1, canvasHeight, false); err != nil {
-			return err
-		}
-		cursor += cw
-	}
-	return nil
-}
-
 func writeFrame(bw *bufio.Writer, name, title, fill string, x, y, w, h float64, depth, fontSize int) error {
 	textStyle := ""
 	labelStyle := ""