1 files changed, 56 insertions, 0 deletions
diff --git a/image.cpp b/image.cpp
new file mode 100644
index 0000000..675e22f
--- /dev/null
+++ b/image.cpp
@@ -0,0 +1,56 @@
+#include "image.h"
+#include <iostream>
+#include <array>
+#include <string>
+#include <cstring>
+#include <cassert>
+#include <cmath>
+#include <png.h>
+
+
+static std::array<uint8_t, 3> render_pixel(double x) {
+	const double red = 1 - std::pow(1 - x, 3);
+	const double green = 1 - std::pow(1 - x, 3);
+	const double blue = 1 - std::pow(1 - x, 6);
+	return {(uint8_t)(red * 255), (uint8_t)(green * 255), (uint8_t)(blue * 255)};
+}
+
+HistImage::HistImage(size_t width, size_t height)
+	: width{width}, height{height}, data(width * height, 0) {}
+
+void HistImage::add(const HistImage &other) {
+	assert(width == other.width && height == other.height);
+	for (size_t i = 0; i < width * height; i++) data[i] += other.data[i];
+}
+
+void HistImage::render(const char *fname) const {
+	uint64_t maxval = 0;
+	for (size_t i = 0; i < width * height; i++) maxval = std::max(maxval, data[i]);
+	const double maxvald = maxval;
+
+	std::vector<uint8_t> buffer(3 * width * height);
+	for (size_t i = 0; i < width * height; i++) {
+		const std::array<uint8_t, 3> pix = render_pixel((double)data[i] / maxvald);
+		memcpy(&buffer[3 * i], &pix[0], 3);
+	}
+
+	png_image png;
+	memset(&png, 0, sizeof png);
+	png.version = PNG_IMAGE_VERSION;
+	png.width = width;
+	png.height = height;
+	png.format = PNG_FORMAT_RGB;
+
+	int ret = png_image_write_to_file(&png, fname, 0, buffer.data(), 3 * width, NULL);
+	if (ret != 0 && (png.warning_or_error & 2)) {
+		std::string errmsg;
+		char *p = (char*)memchr(png.message, ' ', sizeof png.message);
+		if (p != NULL) { errmsg = std::string(png.message, p - png.message); }
+		else errmsg = std::string(png.message, sizeof png.message);
+		std::cerr << "PNG write failed: " << errmsg << std::endl;
+	}
+
+	png_image_free(&png);
+}
+
+// vim: set sw=4 ts=4 noet: