From a233b746c2a0725f0291e131189576cdd09cda36 Mon Sep 17 00:00:00 2001
From: Josh Holtrop <jholtrop@gmail.com>
Date: Wed, 28 Oct 2026 21:28:28 -0400
Subject: [PATCH] Add ImageWriter

---
 src/fart/ImageWriter.cpp | 51 ++++++++++++++++++++++++++++++++++++++++
 src/fart/ImageWriter.h   | 10 ++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 src/fart/ImageWriter.cpp
 create mode 100644 src/fart/ImageWriter.h

diff --git a/src/fart/ImageWriter.cpp b/src/fart/ImageWriter.cpp
new file mode 100644
index 0000000..8848125
--- /dev/null
+++ b/src/fart/ImageWriter.cpp
@@ -0,0 +1,51 @@
+#include <fart/ImageWriter.h>
+#include <png.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <algorithm>
+#include <cmath>
+#include <filesystem>
+#include <vector>
+
+static uint8_t to_byte(double v)
+{
+    return (uint8_t)std::lround(std::clamp(v, 0.0, 1.0) * 255.0);
+}
+
+static bool write_png(const Image & image, const std::string & fname)
+{
+    std::vector<uint8_t> buffer(image.width * image.height * 4u);
+    for (size_t i = 0u; i < image.pixels.size(); i++)
+    {
+        const Color & c = image.pixels[i];
+        buffer[i * 4u + 0u] = to_byte(c.r);
+        buffer[i * 4u + 1u] = to_byte(c.g);
+        buffer[i * 4u + 2u] = to_byte(c.b);
+        buffer[i * 4u + 3u] = to_byte(c.a);
+    }
+
+    png_image png = {};
+    png.version = PNG_IMAGE_VERSION;
+    png.width = image.width;
+    png.height = image.height;
+    png.format = PNG_FORMAT_RGBA;
+
+    if (!png_image_write_to_file(&png, fname.c_str(), 0, buffer.data(), 0, nullptr))
+    {
+        fprintf(stderr, "Error writing PNG file '%s': %s\n", fname.c_str(), png.message);
+        png_image_free(&png);
+        return false;
+    }
+    return true;
+}
+
+bool ImageWriter::write(const Image & image, const std::string & fname)
+{
+    std::string ext = std::filesystem::path(fname).extension().string();
+    if (ext == ".png")
+    {
+        return write_png(image, fname);
+    }
+    fprintf(stderr, "Unsupported output image format: '%s'\n", fname.c_str());
+    return false;
+}
diff --git a/src/fart/ImageWriter.h b/src/fart/ImageWriter.h
new file mode 100644
index 0000000..50387c8
--- /dev/null
+++ b/src/fart/ImageWriter.h
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <string>
+#include <fart/Image.h>
+
+class ImageWriter
+{
+public:
+    static bool write(const Image & image, const std::string & fname);
+};