Behavision/desktop/icons.go

package main

import (
	"bytes"
	"encoding/binary"
	"image"
	"image/color"
	"image/png"
	"runtime"

	agentpaths "github.com/loyaly/behavision-agent/pkg/paths"
)

// iconFor renders the tray icon at run time rather than embedding four PNGs.
//
// A 16x16 filled circle is all the taskbar shows at this size, and generating
// it means the four states cannot drift apart visually or have one file go
// missing from a build.
//
// The encoding is per-platform and is NOT cosmetic. systray writes these bytes
// to a temp file and, on Windows, hands the path to LoadImageW with
// IMAGE_ICON|LR_LOADFROMFILE — which decodes .ico and nothing else. A PNG
// there returns 0, systray logs "unable to set icon", and the product ships
// with no tray icon at all: the one control surface a shop manager has.
func iconFor(state string) []byte {
	img := circle(colorFor(state))
	if runtime.GOOS == "windows" {
		return encodeICO(img)
	}
	var buf bytes.Buffer
	_ = png.Encode(&buf, img)
	return buf.Bytes()
}

// colorFor maps engine state to the only thing the taskbar conveys at 16px.
func colorFor(state string) color.RGBA {
	switch state {
	case "ok":
		return color.RGBA{R: 0x2E, G: 0x9E, B: 0x60, A: 0xFF} // green
	case "warn":
		return color.RGBA{R: 0xE0, G: 0xA3, B: 0x3A, A: 0xFF} // amber
	case "error":
		return color.RGBA{R: 0xD1, G: 0x4B, B: 0x3F, A: 0xFF} // red
	default:
		return color.RGBA{R: 0x86, G: 0x93, B: 0x9E, A: 0xFF} // grey
	}
}

const iconSize = 16

func circle(c color.RGBA) *image.RGBA {
	img := image.NewRGBA(image.Rect(0, 0, iconSize, iconSize))
	const r = 6.5
	cx, cy := float64(iconSize)/2-0.5, float64(iconSize)/2-0.5
	for y := 0; y < iconSize; y++ {
		for x := 0; x < iconSize; x++ {
			dx, dy := float64(x)-cx, float64(y)-cy
			d := dx*dx + dy*dy
			switch {
			case d <= (r-1)*(r-1):
				img.SetRGBA(x, y, c)
			case d <= r*r:
				// One-pixel feathered edge; a hard-aliased circle looks broken
				// next to every other icon in the tray.
				a := uint8(float64(c.A) * (r*r - d) / (r*r - (r-1)*(r-1)))
				img.SetRGBA(x, y, color.RGBA{R: c.R, G: c.G, B: c.B, A: a})
			}
		}
	}
	return img
}

// encodeICO writes a single-image .ico holding an uncompressed 32-bit DIB.
//
// Vista and later also accept a PNG stored inside the .ico container, which
// would be a dozen lines instead of forty. It is not worth the risk: which
// Windows builds accept PNG-in-ICO through LoadImage rather than through the
// newer imaging APIs is genuinely murky, the failure is silent, and it would
// only ever be discovered on a customer's counter. A DIB is what every version
// of Windows has always loaded.
func encodeICO(img *image.RGBA) []byte {
	w, h := img.Bounds().Dx(), img.Bounds().Dy()
	// 1bpp AND mask, each row padded to a 4-byte boundary. Unused with a 32-bit
	// alpha channel, but the format requires it to be present and sized.
	maskRow := ((w + 31) / 32) * 4
	xor := w * h * 4
	dib := 40 + xor + maskRow*h

	var b bytes.Buffer
	// ICONDIR
	binary.Write(&b, binary.LittleEndian, uint16(0)) // reserved
	binary.Write(&b, binary.LittleEndian, uint16(1)) // type: icon
	binary.Write(&b, binary.LittleEndian, uint16(1)) // image count
	// ICONDIRENTRY. 256 is encoded as 0 in these byte fields; at 16px it is moot.
	b.WriteByte(byte(w))
	b.WriteByte(byte(h))
	b.WriteByte(0) // palette size: none
	b.WriteByte(0) // reserved
	binary.Write(&b, binary.LittleEndian, uint16(1))    // colour planes
	binary.Write(&b, binary.LittleEndian, uint16(32))   // bits per pixel
	binary.Write(&b, binary.LittleEndian, uint32(dib))  // bytes in resource
	binary.Write(&b, binary.LittleEndian, uint32(6+16)) // offset to that data

	// BITMAPINFOHEADER. Height is doubled because the DIB nominally stacks the
	// colour image and the AND mask; omitting the doubling renders half an icon
	// stretched over the whole square.
	binary.Write(&b, binary.LittleEndian, uint32(40))
	binary.Write(&b, binary.LittleEndian, int32(w))
	binary.Write(&b, binary.LittleEndian, int32(h*2))
	binary.Write(&b, binary.LittleEndian, uint16(1))
	binary.Write(&b, binary.LittleEndian, uint16(32))
	binary.Write(&b, binary.LittleEndian, uint32(0)) // BI_RGB, uncompressed
	binary.Write(&b, binary.LittleEndian, uint32(xor+maskRow*h))
	for i := 0; i < 4; i++ { // resolution and palette counts, all unused
		binary.Write(&b, binary.LittleEndian, uint32(0))
	}

	// Pixels: BGRA, bottom-up. Go's image is top-down and RGBA, so both the row
	// order and the channel order invert here.
	for y := h - 1; y >= 0; y-- {
		for x := 0; x < w; x++ {
			c := img.RGBAAt(x, y)
			b.Write([]byte{c.B, c.G, c.R, c.A})
		}
	}
	b.Write(make([]byte, maskRow*h)) // all-zero: every pixel opaque per the mask
	return b.Bytes()
}

func logsDir() string { return agentpaths.StateRoot() }