Merge pull request #214 from jbo-ads/image-merge-optimization

Image merge optimization

Author: jbo-ads

include/mapcache.h

@@ -1534,6 +1534,11 @@ void _mapcache_imageio_jpeg_decode_to_image(mapcache_context *ctx, mapcache_buff
  */
 mapcache_image_format_type mapcache_imageio_header_sniff(mapcache_context *ctx, mapcache_buffer *buffer);
 
+/**
+ * \brief lookup the first few bytes of a buffer to check for alpha channel
+ */
+mapcache_image_alpha_type mapcache_imageio_alpha_sniff(mapcache_context *ctx, mapcache_buffer *buffer);
+
 /**
  * \brief checks if the given buffer is a recognized image format
  */

lib/imageio.c

@@ -58,6 +58,43 @@ mapcache_image_format_type mapcache_imageio_header_sniff(mapcache_context *ctx,
   }
 }
 
+mapcache_image_alpha_type mapcache_imageio_alpha_sniff(mapcache_context *ctx, mapcache_buffer *buffer)
+{
+  const unsigned char * b = buffer->buf;
+  mapcache_image_format_type t = mapcache_imageio_header_sniff(ctx,buffer);
+  mapcache_image_alpha_type alpha_type;
+
+  switch (t) {
+    case GC_JPEG:
+      // JPEG files are opaque
+      alpha_type = MC_ALPHA_NO;
+      break;
+    case GC_PNG:
+      if (buffer->size >= 26) {
+        // Check color type of PNG file in IHDR chunk
+        if ( (b[12]|32)=='i' && (b[13]|32)=='h' && (b[14]|32)=='d' && (b[15]|32)=='r' ) {
+          switch (b[25]) {
+            case 4:
+            case 6:
+              // Gray or RGB with alpha
+              alpha_type = MC_ALPHA_YES;
+              break;
+            default:
+              // Other colortypes have no alpha channel
+              alpha_type = MC_ALPHA_NO;
+          }
+        }
+      } else {
+        alpha_type = MC_ALPHA_UNKNOWN;
+      }
+      break;
+    default:
+      alpha_type = MC_ALPHA_UNKNOWN;
+      break;
+  }
+  return alpha_type;
+}
+
 mapcache_image* mapcache_imageio_decode(mapcache_context *ctx, mapcache_buffer *buffer)
 {
   mapcache_image_format_type type = mapcache_imageio_header_sniff(ctx,buffer);

lib/imageio_jpeg.c

@@ -243,6 +243,7 @@ void _mapcache_imageio_jpeg_decode_to_image(mapcache_context *r, mapcache_buffer
     return;
   }
 
+  img->has_alpha = MC_ALPHA_NO;
   jpeg_read_header(&cinfo, TRUE);
   jpeg_start_decompress(&cinfo);
   img->w = cinfo.output_width;

lib/imageio_png.c

@@ -408,6 +408,7 @@ void _mapcache_imageio_png_decode_to_image(mapcache_context *ctx, mapcache_buffe
     unsigned char pixel[4];
     uint8_t  alpha;
     unsigned char *pixptr = row_pointers[i];
+    img->has_alpha = MC_ALPHA_NO;
     for(j=0; j<img->w; j++) {
 
       memcpy (pixel, pixptr, sizeof (uint32_t));
@@ -417,10 +418,12 @@ void _mapcache_imageio_png_decode_to_image(mapcache_context *ctx, mapcache_buffe
         pixptr[1] = pixel[1];
         pixptr[2] = pixel[0];
       } else if (alpha == 0) {
+        img->has_alpha = MC_ALPHA_YES;
         pixptr[0] = 0;
         pixptr[1] = 0;
         pixptr[2] = 0;
       } else {
+        img->has_alpha = MC_ALPHA_YES;
         PREMULTIPLY(pixptr[0],pixel[2],alpha);
         PREMULTIPLY(pixptr[1],pixel[1],alpha);
         PREMULTIPLY(pixptr[2],pixel[0],alpha);

lib/tileset.c

@@ -903,8 +903,8 @@ void mapcache_tileset_tile_set_get_with_subdimensions(mapcache_context *ctx, map
         if(GC_HAS_ERROR(ctx))
           goto cleanup;
       }
-      if((subtile->encoded_data && mapcache_imageio_header_sniff(ctx,subtile->encoded_data) == GC_JPEG)||
-         (subtile->raw_image && subtile->raw_image->has_alpha == MC_ALPHA_NO)) {
+      if ((mapcache_imageio_alpha_sniff(ctx,subtile->encoded_data) == MC_ALPHA_NO) ||
+          (subtile->raw_image && subtile->raw_image->has_alpha == MC_ALPHA_NO)) {
         /* the returned image is fully opaque, we don't need to get/decode/merge any further subtiles */
         if(assembled_image)
           assembled_image->has_alpha = MC_ALPHA_NO;