decode.c

#include "decode.h"
#include "common.h"

static char chars[83] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#$%*+,-.:;=?@[]^_{|}~";

static inline uint8_t clampToUByte(int * src) {
	if( *src >= 0 && *src <= 255 )
		return *src;
	return (*src < 0) ? 0 : 255;
}

static inline uint8_t *  createByteArray(int size) {
	return (uint8_t *)malloc(size * sizeof(uint8_t));
}

int decodeToInt(const char * string, int start, int end) {
	int value = 0, iter1 = 0, iter2 = 0;
	for( iter1 = start; iter1 < end; iter1 ++) {
		int index = -1;
		for(iter2 = 0; iter2 < 83; iter2 ++) {
			if (chars[iter2] == string[iter1]) {
				index = iter2;
				break;
			}
		}
		if (index == -1) return -1;
		value = value * 83 + index;
	}
	return value;
}

bool isValidBlurhash(const char * blurhash) {

	const int hashLength = strlen(blurhash);

	if ( !blurhash || strlen(blurhash) < 6) return false;

	int sizeFlag = decodeToInt(blurhash, 0, 1);	//Get size from first character
	int numY = (int)floorf(sizeFlag / 9) + 1;
	int numX = (sizeFlag % 9) + 1;

	if (hashLength != 4 + 2 * numX * numY) return false;
	return true;
}

void decodeDC(int value, float * r, float * g, float * b) {
	*r = sRGBToLinear(value >> 16); 	// R-component
	*g = sRGBToLinear((value >> 8) & 255); // G-Component
	*b = sRGBToLinear(value & 255);	// B-Component
}

void decodeAC(int value, float maximumValue, float * r, float * g, float * b) {
	int quantR = (int)floorf(value / (19 * 19));
	int quantG = (int)floorf(value / 19) % 19;
	int quantB = (int)value % 19;

	*r = signPow(((float)quantR - 9) / 9, 2.0) * maximumValue;
	*g = signPow(((float)quantG - 9) / 9, 2.0) * maximumValue;
	*b = signPow(((float)quantB - 9) / 9, 2.0) * maximumValue;
}

int decodeToArray(const char * blurhash, int width, int height, int punch, int nChannels, uint8_t * pixelArray) {
	if (! isValidBlurhash(blurhash)) return -1;
	if (punch < 1) punch = 1;

	int sizeFlag = decodeToInt(blurhash, 0, 1);
	int numY = (int)floorf(sizeFlag / 9) + 1;
	int numX = (sizeFlag % 9) + 1;
	int iter = 0;

	float r = 0, g = 0, b = 0;
	int quantizedMaxValue = decodeToInt(blurhash, 1, 2);
	if (quantizedMaxValue == -1) return -1;

	float maxValue = ((float)(quantizedMaxValue + 1)) / 166;

	int colors_size = numX * numY;
	float colors[colors_size][3];

	for(iter = 0; iter < colors_size; iter ++) {
		if (iter == 0) {
			int value = decodeToInt(blurhash, 2, 6);
			if (value == -1) return -1;
			decodeDC(value, &r, &g, &b);
			colors[iter][0] = r;
			colors[iter][1] = g;
			colors[iter][2] = b;

		} else {
			int value = decodeToInt(blurhash, 4 + iter * 2, 6 + iter * 2);
			if (value == -1) return -1;
			decodeAC(value, maxValue * punch, &r, &g, &b);
			colors[iter][0] = r;
			colors[iter][1] = g;
			colors[iter][2] = b;
		}
	}

	int bytesPerRow = width * nChannels;
	int x = 0, y = 0, i = 0, j = 0;
	int intR = 0, intG = 0, intB = 0;

	for(y = 0; y < height; y ++) {
		for(x = 0; x < width; x ++) {

			float r = 0, g = 0, b = 0;

			for(j = 0; j < numY; j ++) {
				for(i = 0; i < numX; i ++) {
					float basics = cos((M_PI * x * i) / width) * cos((M_PI * y * j) / height);
					int idx = i + j * numX;
					r += colors[idx][0] * basics;
					g += colors[idx][1] * basics;
					b += colors[idx][2] * basics;
				}
			}

			intR = linearTosRGB(r);
			intG = linearTosRGB(g);
			intB = linearTosRGB(b);

			pixelArray[nChannels * x + 0 + y * bytesPerRow] = clampToUByte(&intR);
			pixelArray[nChannels * x + 1 + y * bytesPerRow] = clampToUByte(&intG);
			pixelArray[nChannels * x + 2 + y * bytesPerRow] = clampToUByte(&intB);

			if (nChannels == 4)
				pixelArray[nChannels * x + 3 + y * bytesPerRow] = 255;   // If nChannels=4, treat each pixel as RGBA instead of RGB

		}
	}

	return 0;
}

uint8_t * decode(const char * blurhash, int width, int height, int punch, int nChannels) {
	int bytesPerRow = width * nChannels;
	uint8_t * pixelArray = createByteArray(bytesPerRow * height);

	if (decodeToArray(blurhash, width, height, punch, nChannels, pixelArray) == -1)
		return NULL;
	return pixelArray;
}

void freePixelArray(uint8_t * pixelArray) {
	if (pixelArray) {
		free(pixelArray);
	}
}