From e1b3347da56110563324b7b1afb0c38a9d172732 Mon Sep 17 00:00:00 2001
From: Matthias Schiffer <mschiffer@universe-factory.net>
Date: Tue, 3 Feb 2015 12:41:47 +0100
Subject: Start mipmapping infrastructure

---
 src/PNG.cpp | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 81 insertions(+), 4 deletions(-)

(limited to 'src/PNG.cpp')

diff --git a/src/PNG.cpp b/src/PNG.cpp
index 1e25712..0154f61 100644
--- a/src/PNG.cpp
+++ b/src/PNG.cpp
@@ -28,17 +28,19 @@
 
 #include <cerrno>
 #include <cstdio>
+#include <cstring>
 #include <system_error>
 
 #include <png.h>
 
 
 namespace MinedMap {
+namespace PNG {
 
-void writePNG(const char *filename, const uint32_t *data, size_t width, size_t height) {
+void write(const char *filename, const uint8_t *data, size_t width, size_t height) {
 	std::FILE *f = std::fopen(filename, "wb");
 	if (!f)
-		throw std::system_error(errno, std::generic_category(), "unable to open output file");
+		throw std::system_error(errno, std::generic_category(), "unable to open PNG file");
 
 	png_structp png_ptr = png_create_write_struct (PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
 	if (!png_ptr)
@@ -63,13 +65,88 @@ void writePNG(const char *filename, const uint32_t *data, size_t width, size_t h
 
 	uint8_t *row_pointers[height];
 	for (size_t i = 0; i < height; i++)
-		row_pointers[i] = const_cast<uint8_t*>(reinterpret_cast<const uint8_t*>(&data[i*width]));
+		row_pointers[i] = const_cast<uint8_t*>(&data[4*i*width]);
 
 	png_set_rows(png_ptr, info_ptr, row_pointers);
-	png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, NULL);
+	png_write_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, nullptr);
 
 	png_destroy_write_struct(&png_ptr, &info_ptr);
 	std::fclose(f);
 }
 
+void read(const char *filename, uint8_t *data, size_t width, size_t height) {
+	std::FILE *f = std::fopen(filename, "rb");
+	if (!f)
+		throw std::system_error(errno, std::generic_category(), "unable to open PNG file");
+
+	png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, nullptr, nullptr, nullptr);
+	if (!png_ptr)
+		throw std::runtime_error("unable to create PNG read struct");
+
+	png_infop info_ptr = png_create_info_struct(png_ptr);
+	if (!info_ptr) {
+		png_destroy_read_struct(&png_ptr, nullptr, nullptr);
+		throw std::runtime_error("unable to create PNG info struct");
+	}
+
+	png_infop end_info = png_create_info_struct(png_ptr);
+	if (!end_info) {
+		png_destroy_read_struct(&png_ptr, &info_ptr, nullptr);
+		throw std::runtime_error("unable to create PNG info struct");
+	}
+
+	if (setjmp(png_jmpbuf(png_ptr))) {
+		png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
+		fclose(f);
+		throw std::runtime_error("unable to read PNG file");
+	}
+
+	png_init_io(png_ptr, f);
+
+	png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_IDENTITY, nullptr);
+
+	if (png_get_image_width(png_ptr, info_ptr) != width
+	    || png_get_image_height(png_ptr, info_ptr) != height
+	    || png_get_bit_depth(png_ptr, info_ptr) != 8
+	    || png_get_color_type(png_ptr, info_ptr) != PNG_COLOR_TYPE_RGB_ALPHA)
+		longjmp(png_jmpbuf(png_ptr), 1);
+
+	uint8_t **row_pointers = png_get_rows(png_ptr, info_ptr);
+	for (size_t i = 0; i < height; i++)
+		std::memcpy(&data[4*i*width], row_pointers[i], 4*width);
+
+	png_destroy_read_struct(&png_ptr, &info_ptr, &end_info);
+	std::fclose(f);
+}
+
+static void readScaled(uint8_t *data, size_t offset_w, size_t offset_h, const char *file, size_t width, size_t height) {
+	if (!file)
+		return;
+
+	uint8_t input[4*width*height];
+	read(file, input, width, height);
+
+	for (size_t h = 0; h < width/2; h++) {
+		for (size_t w = 0; w < width/2; w++) {
+			for (size_t c = 0; c < 4; c++) {
+				size_t i = 8*width*h + 8*w + c;
+				data[4*width*(offset_h+h) + 4*(offset_w+w) + c] = (input[i] + input[i+4] + input[i+4*width] + input[i+4*width+4])/4;
+			}
+		}
+	}
+}
+
+void mipmap(const char *output, size_t width, size_t height, const char *nw, const char *ne, const char *sw, const char *se) {
+	uint8_t data[4*width*height];
+	std::memset(data, 0, sizeof(data));
+
+	readScaled(data, 0, 0, nw, width, height);
+	readScaled(data, width/2, 0, ne, width, height);
+	readScaled(data, 0, height/2, sw, width, height);
+	readScaled(data, width/2, height/2, se, width, height);
+
+	write(output, data, width, height);
+}
+
+}
 }
-- 
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