1 files changed, 140 insertions, 0 deletions
diff --git a/mons_image/src/qoi.c b/mons_image/src/qoi.c
new file mode 100644
index 0000000..c290c4e
--- /dev/null
+++ b/mons_image/src/qoi.c
@@ -0,0 +1,140 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <byteswap.h>
+#include <inttypes.h>
+#include "qoi.h"
+#include "image.h"
+
+#define MONS_QOI_RGB 3
+#define MONS_QOI_RGBA 4
+#define MONS_QOI_SRGB_LINEAR_ALPHA 0
+#define MONS_QOI_LINEAR 1
+#define MONS_QOI_HEADER_LEN 14
+
+#define MONS_QOI_OP_RGB 0b11111110
+#define MONS_QOI_OP_RGBA 0b11111111
+#define MONS_QOI_OP_INDEX 0b00000000
+#define MONS_QOI_OP_DIFF 0b01000000
+#define MONS_QOI_OP_LUMA 0b10000000
+#define MONS_QOI_OP_RUN 0b11000000
+
+typedef struct mons_qoi_header {
+    char magic[4];
+    uint32_t width;
+    uint32_t height;
+    uint8_t channels;
+    uint8_t colorspace;
+} mons_qoi_header;
+
+unsigned char pixel_index_hash(mons_pixel pixel) {
+    return (pixel.r * 3 + pixel.g * 5 + pixel.b * 7 + pixel.a * 11) % 64;
+}
+
+mons_image mons_load_qoi(FILE *stream) {
+    mons_qoi_header header;
+    if (fread(&header, MONS_QOI_HEADER_LEN, 1, stream) != 1) {
+        fprintf(stderr, "Error reading QOI header");
+        return (mons_image){0};
+    }
+    header.width = __bswap_32(header.width);
+    header.height = __bswap_32(header.height);
+    mons_pixel previous = {0, 0, 0, 255};
+    mons_pixel previously_seen[64] = {0};
+    mons_image output = {
+        .width = header.width,
+        .height = header.height,
+        .data = calloc(4, header.width * header.height),
+    };
+    for (size_t i = 0; i < header.width * header.height; i++) {
+        unsigned char op;
+        if (fread(&op, 1, 1, stream) != 1) {
+            fprintf(stderr, "Failed reading operation byte!");
+            return (mons_image){0};
+        }
+        switch (op) {
+        case MONS_QOI_OP_RGB: {
+            unsigned char rgb[3];
+            if (fread(&rgb, 1, 3, stream) != 3) {
+                fprintf(stderr, "Failed reading RGB data!");
+                return (mons_image){0};
+            }
+            output.data[i] = (mons_pixel){
+                .r = rgb[0],
+                .g = rgb[1],
+                .b = rgb[2],
+                .a = previous.a,
+            };
+            break;
+        }
+        case MONS_QOI_OP_RGBA: {
+            unsigned char rgba[4];
+            if (fread(&rgba, 1, 4, stream) != 4) {
+                fprintf(stderr, "Failed reading RGBA data!");
+                return (mons_image){0};
+            }
+            output.data[i] = (mons_pixel){
+                .r = rgba[0],
+                .g = rgba[1],
+                .b = rgba[2],
+                .a = rgba[3],
+            };
+            break;
+        }
+        default:
+            switch (op & 0b11000000) {
+            case MONS_QOI_OP_INDEX: {
+                unsigned char index = op & 0b00111111;
+                output.data[i] = previously_seen[index];
+                break;
+            }
+            case MONS_QOI_OP_DIFF: {
+                char r_diff = ((op & 0b00110000) >> 4) - 2;
+                char g_diff = ((op & 0b00001100) >> 2) - 2;
+                char b_diff = (op & 0b00000011) - 2;
+                output.data[i] = (mons_pixel){
+                    .r = previous.r + r_diff,
+                    .g = previous.g + g_diff,
+                    .b = previous.b + b_diff,
+                    .a = previous.a,
+                };
+                break;
+            }
+            case MONS_QOI_OP_LUMA: {
+                int g_diff = (op & 0b00111111) - 32;
+                unsigned char second_byte;
+                if (fread(&second_byte, 1, 1, stream) != 1) {
+                    fprintf(stderr,
+                            "Failed to read second byte of luma operation!");
+                    return (mons_image){0};
+                }
+                int r_diff = g_diff - 8 + (((second_byte & 0b11110000) >> 4));
+                int b_diff = g_diff - 8 + (second_byte & 0b00001111);
+                output.data[i] = (mons_pixel){
+                    .r = previous.r + r_diff,
+                    .g = previous.g + g_diff,
+                    .b = previous.b + b_diff,
+                    .a = previous.a,
+                };
+                break;
+            }
+            case MONS_QOI_OP_RUN: {
+                unsigned char run = (op & 0b00111111) + 1;
+                for (int j = 0; j < run; j++) {
+                    output.data[i++] = previous;
+                }
+                i--;
+                break;
+            }
+            default:
+                break;
+            }
+            break;
+        }
+        previous = output.data[i];
+        unsigned int hash = pixel_index_hash(output.data[i]);
+        previously_seen[hash] = output.data[i];
+    }
+    fclose(stream);
+
+    return output;
+}