use hdr_demo as binary name/dir

.github/workflows/include.yml

@@ -23,8 +23,8 @@ jobs:
         uses: fortio/workflows/.github/workflows/releaser.yml@main
         with:
             description: "Support for high dynamic range synthetic PNG image in go"
-            binary_name: "demo"
-            main_path: "./demo"
+            binary_name: "hdr_demo"
+            main_path: "./hdr_demo"
             dockerfile: "./Dockerfile"
         secrets:
             GH_PAT: ${{ secrets.GH_PAT }}

Dockerfile

@@ -1,4 +1,5 @@
 FROM scratch
-COPY demo /usr/bin/demo
+COPY hdr_demo /usr/bin/hdr_demo
 ENV HOME=/home/user
-ENTRYPOINT ["/usr/bin/demo"]
+WORKDIR /home/user
+ENTRYPOINT ["/usr/bin/hdr_demo"]

Makefile

@@ -16,6 +16,6 @@ coverage:
 	go test -race -coverprofile=coverage.out -covermode=atomic ./...
 
 demo:
-	go run ./demo
+	go run ./hdr_demo
 
 .PHONY: lint coverage test demo all

README.md

@@ -19,29 +19,48 @@ HDR:
 ![Mandelbrot HDR](mandelbrot_hdr.png)
 
 ## Install
-You can get the binary from [releases](https://github.com/fortio/hdr/releases)
+Use in your own code importing "fortio.org/hdr" and Encode() away.
+
+You can get the demo binary from [releases](https://github.com/fortio/hdr/releases)
 
 Or just run
 ```
-CGO_ENABLED=0 go install fortio.org/hdr/demo@latest  # to install (in ~/go/bin typically) or just
-CGO_ENABLED=0 go run fortio.org/hdr@latest  # to run without install
+CGO_ENABLED=0 go install fortio.org/hdr/hdr_demo@latest  # to install (in ~/go/bin typically) or just
+CGO_ENABLED=0 go run fortio.org/hdr/hdr_demo@latest  # to run without install
 ```
 
 or
 ```
-brew install fortio/tap/hdr
+brew install fortio/tap/hdr_demo
 ```
 
 or
 ```
-docker run -ti fortio/hdr
+docker run -ti -v `pwd`:/home/user fortio/hdr_demo
 ```
 
 
 ## Usage
 
 ```
-hdr help
-
+$ hdr_demo help
+hdr_demo v1.0.0 usage:
+        hdr_demo [flags]
+or 1 of the special arguments
+        hdr_demo {help|envhelp|version|buildinfo}
 flags:
+  -chroma float
+        chroma (saturation) for coloring (default 80)
+  -hue-freq float
+        hue frequency multiplier for coloring (higher means more color cycles) (default 0.35)
+  -light-angle float
+        light angle in degrees for shading (azimuth) (default 45)
+  -light-height float
+        light height for shading (elevation, higher means more light from above) (default 1.5)
+  -profile-cpu file
+        write cpu profile to file
+  -profile-mem file
+        write memory profile to file
+  -shading float
+        range for shading lightness (0 = no shading, 100 = full range from black to white) (default 70)
 ```

hdr.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"compress/zlib"
 	"encoding/binary"
+	"fmt"
 	"hash/crc32"
 	"image"
 	"io"
@@ -180,21 +181,22 @@ func sumAbs(data []byte) int64 {
 	return s
 }
 
-// Encode writes img as a PNG (truecolor 16-bit per channel with alpha) to w.
-// Adaptive row filtering (None/Sub/Up/Average/Paeth) is used to minimize file size.
-//
+// Encode writes img as an HDR PNG 3.0 (truecolor 16-bit per channel with alpha) to the provided writer.
 // The white parameter controls HDR output (PNG 3.0 with cICP chunk):
 //   - white == 0 : standard sRGB PNG (no HDR metadata).
 //   - white in (0,1] : HDR PQ PNG.  Input pixels at this sRGB intensity
 //     map to SDR reference white (203 nits); brighter pixels extend into
 //     the HDR range.  For example white=0.5 means anything above 50 %
 //     input brightness will appear brighter than SDR white on HDR displays.
-func Encode(w io.Writer, img *image.NRGBA64, white float64) error {
+func Encode(writer io.Writer, img *image.NRGBA64, white float64) error {
 	bounds := img.Bounds()
 	width := bounds.Dx()
 	height := bounds.Dy()
+	if white < 0 || white > 1 {
+		return fmt.Errorf("white parameter must be in [0,1], got %f", white)
+	}
 	// PNG signature
-	if _, err := w.Write(pngSignature[:]); err != nil {
+	if _, err := writer.Write(pngSignature[:]); err != nil {
 		return err
 	}
 	// IHDR
@@ -203,7 +205,7 @@ func Encode(w io.Writer, img *image.NRGBA64, white float64) error {
 	binary.BigEndian.PutUint32(ihdr[4:8], safecast.MustConv[uint32](height))
 	ihdr[8] = 16 // bit depth: 16 bits per channel
 	ihdr[9] = 6  // color type: truecolor with alpha (RGBA)
-	if err := writeChunk(w, "IHDR", ihdr[:]); err != nil {
+	if err := writeChunk(writer, "IHDR", ihdr[:]); err != nil {
 		return err
 	}
 	// HDR mode: add cICP chunk (PNG 3.0) signaling BT.2020 + PQ.
@@ -216,7 +218,7 @@ func Encode(w io.Writer, img *image.NRGBA64, white float64) error {
 			0,  // Matrix coefficients: Identity
 			1,  // Video full range flag
 		}
-		if err := writeChunk(w, "cICP", cicp[:]); err != nil {
+		if err := writeChunk(writer, "cICP", cicp[:]); err != nil {
 			return err
 		}
 		// scaleFactor maps srgbToLinear(white) → SDR reference white in PQ's
@@ -272,9 +274,9 @@ func Encode(w io.Writer, img *image.NRGBA64, white float64) error {
 	if err := zw.Close(); err != nil {
 		return err
 	}
-	if err := writeChunk(w, "IDAT", buf.Bytes()); err != nil {
+	if err := writeChunk(writer, "IDAT", buf.Bytes()); err != nil {
 		return err
 	}
 	// IEND
-	return writeChunk(w, "IEND", nil)
+	return writeChunk(writer, "IEND", nil)
 }