improved support for PNG images

image_read.cpp

@@ -116,9 +116,9 @@ unsigned char *FileRead::pngRead(const char *texturePath,
     }
     // initialize
     png_structp png_ptr=png_create_read_struct(PNG_LIBPNG_VER_STRING,
-                                               NULL,//(png_voidp)user_error_ptr,
-                                               NULL,//user_error_fn,
-                                               NULL);//user_warning_fn);
+                                               NULL,
+                                               NULL,
+                                               NULL);
     if(!png_ptr){
         fprintf(stderr,"error reading %s\n",texturePath);
         exit(-1);
@@ -139,40 +139,68 @@ unsigned char *FileRead::pngRead(const char *texturePath,
     *outImageWidth=png_get_image_width(png_ptr,info_ptr);
     *outImageHeight=png_get_image_height(png_ptr,info_ptr);
     png_byte color_type=png_get_color_type(png_ptr,info_ptr);
-    if(color_type!=PNG_COLOR_TYPE_RGB){
-            fprintf(stderr,"color type of %s must be RGB\n",texturePath);
-            // TODO: at this moment, it is only implemented reading RGB images
-            exit(-1);
+    png_byte bit_depth=png_get_bit_depth(png_ptr,info_ptr);
+    if(bit_depth==16)
+        png_set_strip_16(png_ptr);
+    if(bit_depth<8)
+        png_set_expand_gray_1_2_4_to_8(png_ptr);
+    if(color_type==PNG_COLOR_TYPE_GRAY||color_type==PNG_COLOR_TYPE_GRAY_ALPHA)
+        png_set_gray_to_rgb(png_ptr);
+    if(color_type==PNG_COLOR_TYPE_PALETTE){
+        png_set_palette_to_rgb(png_ptr);
+        // TODO: Read the transparency values for indexed images;
+        // currently, they are ignored by stripping the alpha information.
+        png_set_strip_alpha(png_ptr);
     }
-    // TODO: set the value of depth according to the color type
-    int depth=3;        // RGB
-    //png_byte bit_depth=png_get_bit_depth(png_ptr,info_ptr);
-    //int number_of_passes=png_set_interlace_handling(png_ptr);
     png_read_update_info(png_ptr,info_ptr);
     // allocate memory to store the texture
     unsigned char *textureBytes=
             (unsigned char*)malloc((*outImageWidth)*
                                    (*outImageHeight)*
-                                   depth*
+                                   3* // RGB
                                    sizeof(unsigned char));
     // read the contents of the file
     if(setjmp(png_jmpbuf(png_ptr))){
         fprintf(stderr,"error reading %s\n",texturePath);
         exit(-1);
     }
+    // TODO: we can avoid writing in row_pointers[] and later copying to
+    // the texture.
     png_bytep *row_pointers=
             (png_bytep*)malloc(sizeof(png_bytep)*(*outImageHeight));
     for(int y=0;y<(*outImageHeight);++y)
         row_pointers[y]=(png_byte*)malloc(png_get_rowbytes(png_ptr,info_ptr));
     png_read_image(png_ptr,row_pointers);
-    for(int row=0;row<(*outImageHeight);++row){
-        for(int j=0;j<(*outImageWidth);++j){
-            for(int k=0;k<depth;++k){
-                textureBytes[row*(*outImageWidth)*depth+j*depth+k]=
-                    row_pointers[(*outImageHeight)-row-1][j*depth+k];
-            }
-        }
+    switch(color_type){
+    case PNG_COLOR_TYPE_GRAY:
+    case PNG_COLOR_TYPE_PALETTE:
+    case PNG_COLOR_TYPE_RGB:
+        // RGB: copy directly RGB bits to the texture.
+        for(int row=0;row<(*outImageHeight);++row)
+            for(int j=0;j<(*outImageWidth);++j)
+                for(int k=0;k<3;++k)
+                        textureBytes[row*(*outImageWidth)*3+j*3+k]=
+                            row_pointers[(*outImageHeight)-row-1][j*3+k];
+        break;
+    case PNG_COLOR_TYPE_GRAY_ALPHA:
+    case PNG_COLOR_TYPE_RGB_ALPHA:
+        // RGBA: multiply each one of the three first bytes (channels R, G
+        // and B), by the alpha (the fourth byte).
+        for(int row=0;row<(*outImageHeight);++row)
+            for(int j=0;j<(*outImageWidth);++j)
+                for(int k=0;k<3;++k)
+                        textureBytes[row*(*outImageWidth)*3+j*3+k]=
+                            (double)
+                            row_pointers[(*outImageHeight)-row-1][j*4+k]*
+                            row_pointers[(*outImageHeight)-row-1][j*4+3]/
+                            255;
+        break;
+    default:
+        fprintf(stderr,"%s: unrecognized PNG type\n",texturePath);
+        exit(-1);
     }
+    png_read_end(png_ptr,NULL);
+    png_destroy_read_struct(&png_ptr,&info_ptr,NULL);
     for(int row=0;row<(*outImageHeight);++row)
             free(row_pointers[row]);
     free(row_pointers);