libpng loader: expand 1/2/4bpp palette to 8bpp (for issue #29)

saitoha · Feb 15, 2015 · b6748d1 · b6748d1
1 parent 80ec152
commit b6748d1
Showing 1 changed file with 60 additions and 4 deletions.
diff --git a/converters/loader.c b/converters/loader.c
@@ -302,6 +302,45 @@ read_png(png_structp png_ptr, png_bytep data, png_size_t length)
 }
 
 
+static void
+expand_palette(unsigned char *dst, unsigned char *src,
+               int length, int bitdepth)
+{
+    int i;
+
+    switch (bitdepth) {
+    case 1:
+        for (i = 0; i < length / 8; ++i, ++src) {
+            *dst++ = *src >> 7;
+            *dst++ = *src >> 6 & 0x1;
+            *dst++ = *src >> 5 & 0x1;
+            *dst++ = *src >> 4 & 0x1;
+            *dst++ = *src >> 3 & 0x1;
+            *dst++ = *src >> 2 & 0x1;
+            *dst++ = *src >> 1 & 0x1;
+            *dst++ = *src & 0x1;
+        }
+        break;
+    case 2:
+        for (i = 0; i < length / 4; ++i, ++src) {
+            *dst++ = *src >> 6;
+            *dst++ = *src >> 4 & 0x3;
+            *dst++ = *src >> 2 & 0x3;
+            *dst++ = *src & 0x3;
+        }
+        break;
+    case 4:
+        for (i = 0; i < length / 2; ++i, ++src) {
+            *dst++ = *src >> 4;
+            *dst++ = *src & 0xf;
+        }
+        break;
+    default:
+        break;
+    }
+}
+
+
 static unsigned char *
 load_png(unsigned char *buffer, int size,
          int *psx, int *psy, int *pcomp,
@@ -310,14 +349,15 @@ load_png(unsigned char *buffer, int size,
          int *pixelformat)
 {
     chunk_t read_chunk;
-    png_uint_32 bitdepth;
+    png_uint_32 bitdepth = 8;
     png_uint_32 palette_bitdepth;
     png_structp png_ptr;
     png_infop info_ptr;
     unsigned char **rows = NULL;
     unsigned char *result = NULL;
     png_color *png_palette = NULL;
     int i;
+    unsigned char *new_result = NULL;
 
     png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
     if (!png_ptr) {
@@ -343,7 +383,7 @@ load_png(unsigned char *buffer, int size,
     switch (png_get_color_type(png_ptr, info_ptr)) {
     case PNG_COLOR_TYPE_PALETTE:
         palette_bitdepth = png_get_PLTE(png_ptr, info_ptr, &png_palette, pncolors);
-        if (ppalette && png_palette && bitdepth == 8 && palette_bitdepth == 8 && *pncolors <= reqcolors) {
+        if (ppalette && png_palette && palette_bitdepth == 8 && *pncolors <= reqcolors) {
             *ppalette = malloc(*pncolors * 3);
             if (*ppalette == NULL) {
                 goto cleanup;
@@ -418,8 +458,17 @@ load_png(unsigned char *buffer, int size,
     }
     result = malloc(*pcomp * *psx * *psy);
     rows = malloc(*psy * sizeof(unsigned char *));
-    for (i = 0; i < *psy; ++i) {
-        rows[i] = result + *pcomp * *psx * i;
+    switch (*pixelformat) {
+    case PIXELFORMAT_PAL8:
+        for (i = 0; i < *psy; ++i) {
+            rows[i] = result + *pcomp * *psx * i * bitdepth / 8;
+        }
+        break;
+    default:
+        for (i = 0; i < *psy; ++i) {
+            rows[i] = result + *pcomp * *psx * i;
+        }
+        break;
     }
 #if USE_SETJMP && HAVE_SETJMP
     if (setjmp(png_jmpbuf(png_ptr))) {
@@ -433,6 +482,13 @@ load_png(unsigned char *buffer, int size,
     png_destroy_read_struct(&png_ptr, &info_ptr,(png_infopp)0);
     free(rows);
 
+    if (*pixelformat == PIXELFORMAT_PAL8 && bitdepth < 8) {
+        new_result = malloc(*psx * *psy);
+        expand_palette(new_result, result, *psx * *psy, bitdepth);
+        free(result);
+        result = new_result;
+    }
+
     return result;
 }
 # endif  /* HAVE_PNG */