JuliusBrussee/caveman · error

encodeGrayPNG: pixels length %d != %dx%d

Error message

encodeGrayPNG: pixels length %d != %dx%d

What it means

Raised by encodeGrayPNG: the grayscale pixel buffer length does not equal width*height. It is a caller-contract guard in the PNG rasterizer — the pixel slice was built with different dimensions than passed, so encoding would read out of bounds or truncate rows.

Source

Thrown at engine/pixel/png.go:27

	"image/color"
	"image/png"
)

type RenderedImage struct {
	PNG               []byte
	Width, Height     int
	CharsRendered     int
	DroppedChars      int
	DroppedCodepoints map[rune]int
	// Layers is the number of interleaved text layers baked into this image: 1
	// for an ordinary page, 2 for a max-level red/blue overlay page. Zero is
	// treated as 1 by callers (existing single-layer renderers leave it unset).
	Layers int
}

func encodeGrayPNG(pixels []uint8, width, height int) ([]byte, error) {
	if len(pixels) != width*height {
		return nil, fmt.Errorf("encodeGrayPNG: pixels length %d != %dx%d", len(pixels), width, height)
	}
	img := image.NewGray(image.Rect(0, 0, width, height))
	copy(img.Pix, pixels)
	var buf bytes.Buffer
	if err := png.Encode(&buf, img); err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func encodeRGBPNG(pixels []uint8, width, height int) ([]byte, error) {
	if len(pixels) != width*height*3 {
		return nil, fmt.Errorf("encodeRGBPNG: pixels length %d != %dx%dx3", len(pixels), width, height)
	}
	img := image.NewNRGBA(image.Rect(0, 0, width, height))
	for i := 0; i < width*height; i++ {
		img.SetNRGBA(i%width, i/width, color.NRGBA{
			R: pixels[i*3],

View on GitHub (pinned to 766dce6b13)

Solutions

1. Ensure the pixel slice has exactly width*height entries before calling encodeGrayPNG
2. Allocate pixels with make([]uint8, width*height) at the same dimensions passed to the renderer
3. Fix the renderer that produced a mismatched buffer (check stride/row padding)

When it happens

Trigger: Thrown at engine/pixel/png.go:27 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of JuliusBrussee/caveman@766dce6b13 (2026-08-18). Data as JSON: /api/errors/f6936d664807ae37. Report an issue: GitHub.