6.6.3 - Alpha5 - images.save 方法使用 quality 参数时支持 png 格式的文件体积压缩 (issue #367)

libs/imagequant/external/libimagequant/example.c

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+/**
+
+This is an example how to write your own simple pngquant using libimagequant.
+
+libimagequant works with any PNG library. This example uses lodepng, because it's easier to use than libpng.
+
+To run this example, run these commands in the library directory:
+
+    make example
+    ./example /path/to/some_file.png
+
+On "manually":
+
+1. Get lodepng.c (download lodepng.cpp and rename it) and lodepng.h
+   from http://lodev.org/lodepng/ and put them in this directry
+
+2. Compile libimagequant (see README.md)
+
+3. Compile and run the example:
+
+   gcc -O3 example.c libimagequant.a -o example
+   ./example truecolor_file.png
+
+
+This example code can be freely copied under CC0 (public domain) license.
+*/
+
+#include "lodepng.h" // Get it from https://raw.githubusercontent.com/lvandeve/lodepng/master/lodepng.h
+#include "lodepng.c" // Get it from https://raw.githubusercontent.com/lvandeve/lodepng/master/lodepng.cpp and rename
+#include <stdio.h>
+#include <stdlib.h>
+#include "libimagequant.h"
+
+int main(int argc, char *argv[]) {
+    if (argc < 2) {
+        fprintf(stderr, "Please specify a path to a PNG file\n");
+        return EXIT_FAILURE;
+    }
+
+    const char *input_png_file_path = argv[1];
+
+    // Load PNG file and decode it as raw RGBA pixels
+    // This uses lodepng library for PNG reading (not part of libimagequant)
+
+    unsigned int width, height;
+    unsigned char *raw_rgba_pixels;
+    unsigned int status = lodepng_decode32_file(&raw_rgba_pixels, &width, &height, input_png_file_path);
+    if (status) {
+        fprintf(stderr, "Can't load %s: %s\n", input_png_file_path, lodepng_error_text(status));
+        return EXIT_FAILURE;
+    }
+
+    // Use libimagequant to make a palette for the RGBA pixels
+
+    liq_attr *handle = liq_attr_create();
+    liq_image *input_image = liq_image_create_rgba(handle, raw_rgba_pixels, width, height, 0);
+    // You could set more options here, like liq_set_quality
+    liq_result *quantization_result;
+    if (liq_image_quantize(input_image, handle, &quantization_result) != LIQ_OK) {
+        fprintf(stderr, "Quantization failed\n");
+        return EXIT_FAILURE;
+    }
+
+    // Use libimagequant to make new image pixels from the palette
+
+    size_t pixels_size = width * height;
+    unsigned char *raw_8bit_pixels = malloc(pixels_size);
+    liq_set_dithering_level(quantization_result, 1.0);
+
+    liq_write_remapped_image(quantization_result, input_image, raw_8bit_pixels, pixels_size);
+    const liq_palette *palette = liq_get_palette(quantization_result);
+
+    // Save converted pixels as a PNG file
+    // This uses lodepng library for PNG writing (not part of libimagequant)
+
+    LodePNGState state;
+    lodepng_state_init(&state);
+    state.info_raw.colortype = LCT_PALETTE;
+    state.info_raw.bitdepth = 8;
+    state.info_png.color.colortype = LCT_PALETTE;
+    state.info_png.color.bitdepth = 8;
+
+    for(int i=0; i < palette->count; i++) {
+        lodepng_palette_add(&state.info_png.color, palette->entries[i].r, palette->entries[i].g, palette->entries[i].b, palette->entries[i].a);
+        lodepng_palette_add(&state.info_raw, palette->entries[i].r, palette->entries[i].g, palette->entries[i].b, palette->entries[i].a);
+    }
+
+    unsigned char *output_file_data;
+    size_t output_file_size;
+    unsigned int out_status = lodepng_encode(&output_file_data, &output_file_size, raw_8bit_pixels, width, height, &state);
+    if (out_status) {
+        fprintf(stderr, "Can't encode image: %s\n", lodepng_error_text(out_status));
+        return EXIT_FAILURE;
+    }
+
+    const char *output_png_file_path = "quantized_example.png";
+    FILE *fp = fopen(output_png_file_path, "wb");
+    if (!fp) {
+        fprintf(stderr, "Unable to write to %s\n", output_png_file_path);
+        return EXIT_FAILURE;
+    }
+    fwrite(output_file_data, 1, output_file_size, fp);
+    fclose(fp);
+
+    printf("Written %s\n", output_png_file_path);
+
+    // Done. Free memory.
+
+    liq_result_destroy(quantization_result); // Must be freed only after you're done using the palette
+    liq_image_destroy(input_image);
+    liq_attr_destroy(handle);
+
+    free(raw_8bit_pixels);
+    lodepng_state_cleanup(&state);
+}