Add reading alpha

src/tiff/tiffread.c

@@ -27,6 +27,9 @@
 #define NULL_TIFF_IMAGE ((TiffImage){0})
 #define IS_NULL_IMAGE(IMG) (IMG.type == TIFF_IMAGE_TYPE_INVALID)
 
+#define NULL_TIFF_ALPHA ((TiffAlpha){0})
+#define IS_NULL_ALPHA(ALPHA) (ALPHA.type == ALPHA_TYPE_UNDEFINED)
+
 #define INVALID_SAMPLE_COUNT 0
 #define INVALID_ROWS_PER_STRIP 0
 #define INVALID_STRIP_COUNT 0
@@ -59,6 +62,7 @@ struct strip_data_field {
 internal TiffHdr read_tiff_header(const TiffReader *reader);
 internal TiffIFD read_ifd(const TiffReader *reader, Arena *arena);
 internal TiffImage read_ifd_fields(const TiffReader *reader);
+internal TiffAlpha read_alpha(const TiffReader *reader, TiffImage *img);
 internal Pixel *load_image_pixels(TiffReader *reader, Arena *arena);
 internal bool read_strip_data(TiffReader *reader, Arena *arena);
 internal void read_strips(const TiffReader *reader, Pixel *buf);
@@ -253,11 +257,14 @@ internal TiffImage read_ifd_fields(const TiffReader *reader) {
     goto READ_FIELDS_RETURN_IMAGE;
   }
 
+  img_out.alpha = read_alpha(reader, &img_out);
+
 #ifdef DEBUG
   // clang-format off
   printf("SIZE (width, height)                          :   %u, %u\n", img_out.image_width, img_out.image_length);
   printf("SAMPLES (bits per sample, count, is offset)   :   %u, %u, %u\n", img_out.bits_per_sample, img_out.sample_count, img_out.bits_per_sample_offset);
   printf("EXTRA SAMPLES (samples, count, is offset)     :   %u, %u, %u\n", img_out.extra_samples, img_out.extra_samples_count, img_out.extra_samples_offset);
+  printf("ALPHA (type, offset)                          :   %u, %u\n", img_out.alpha.type, img_out.alpha.sample_offset);
   printf("SAMPLES PER PIXEL                             :   %u\n", img_out.sample_count);
   printf("PHOTOMETRIC INTERPRETATION                    :   %u\n", img_out.photometric_interpretation);
   printf("ROWS PER STRIP (rows, strip count)            :   %u, %u\n", img_out.rows_per_strip, img_out.strip_count);
@@ -270,6 +277,39 @@ READ_FIELDS_RETURN_IMAGE:
   return img_out;
 }
 
+internal TiffAlpha read_alpha(const TiffReader *reader, TiffImage *img) {
+  TiffAlpha alpha = NULL_TIFF_ALPHA;
+  u16 samples[img->extra_samples_count];
+
+  if (img->extra_samples_count == 0) {
+    goto READ_ALPHA_RETURN;
+  }
+
+  u64 byte_count = TIFF_SHORT_BYTE_COUNT * img->extra_samples_count;
+  memset(samples, 0, byte_count);
+
+  if (img->extra_samples_offset) {
+    read_from_file_with_offset(reader->fp, samples, byte_count,
+                               img->extra_samples);
+  } else {
+    memcpy(samples, &(img->extra_samples), byte_count);
+  }
+
+  for (u32 i = 0; i < img->extra_samples_count; ++i) {
+    u16 *sample = &(samples[i]);
+    if (*sample == TIFF_EXTRA_SAMPLE_ASSOCIATED_ALPHA ||
+        *sample == TIFF_EXTRA_SAMPLE_UNASSOCIATED_ALPHA) {
+      alpha.type = *sample == TIFF_EXTRA_SAMPLE_ASSOCIATED_ALPHA
+                       ? ALPHA_TYPE_ASSOCIATED
+                       : ALPHA_TYPE_UNASSOCIATED;
+      break;
+    }
+  }
+
+READ_ALPHA_RETURN:
+  return alpha;
+}
+
 internal Pixel *load_image_pixels(TiffReader *reader, Arena *arena) {
   Pixel *buf = NULL;
   u64 img_byte_count =
@@ -345,17 +385,27 @@ internal bool read_strip_data(TiffReader *reader, Arena *arena) {
 
 internal void read_strips(const TiffReader *reader, Pixel *buf) {
   u64 position = 0;
+  u64 main_samples = reader->img.sample_count - reader->img.extra_samples_count;
+  TiffAlpha alpha = reader->img.alpha;
+
+  Pixel *p;
+  u64 start_offset;
+  u64 alpha_offset;
+
   for (u64 i = 0; i < reader->img.strip_count; ++i) {
     const TiffStrip *strip = &(reader->img.strips[i]);
 
     for (u64 j = 0; j < strip->byte_count / reader->img.sample_count; ++j) {
-      Pixel *p = &(buf[position]);
+      p = &(buf[position]);
+      start_offset = strip->offset + j * reader->img.sample_count;
+      alpha_offset = start_offset + main_samples + alpha.sample_offset;
 
-      read_from_file_with_offset(reader->fp, p, reader->img.sample_count,
-                                 strip->offset + j * reader->img.sample_count);
+      read_from_file_with_offset(reader->fp, p, main_samples, start_offset);
 
-      if (reader->img.sample_count == 3) {
+      if (alpha.type == ALPHA_TYPE_UNDEFINED) {
         p->a = 255;
+      } else {
+        read_from_file_with_offset(reader->fp, &(p->a), 1, alpha_offset);
       }
 
       ++position;

src/tiff/tiffread.h

@@ -111,6 +111,18 @@ struct IFD {
   u32 next_ifd;
 };
 
+typedef enum {
+  ALPHA_TYPE_UNDEFINED = 0,
+  ALPHA_TYPE_ASSOCIATED,
+  ALPHA_TYPE_UNASSOCIATED,
+} AlphaType;
+
+typedef struct tiff_alpha TiffAlpha;
+struct tiff_alpha {
+  AlphaType type;
+  u32 sample_offset;
+};
+
 typedef struct tiff_strip TiffStrip;
 struct tiff_strip {
   u32 offset;
@@ -139,6 +151,7 @@ struct tiff_image {
   u32 extra_samples;
   u32 extra_samples_count;
   bool extra_samples_offset;
+  TiffAlpha alpha;
   TiffStrip *strips;
 };