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image viewer: add quick guide describing how to add image decoder. also improve comments.

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git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29066 a1c6a512-1295-4272-9138-f99709370657
This commit is contained in:
Teruaki Kawashima 2011-01-16 12:45:11 +00:00
parent 5c09844d54
commit 62207228f7
2 changed files with 50 additions and 8 deletions
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21
apps/plugins/imageviewer/imageviewer.h
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@ -469,19 +469,24 @@ struct imgdec_api {
/* functions need to be implemented in each image decoders. */
struct image_decoder {
/* if unscaled image can be always displayed when there isn't enough memory
* for resized image. e.g. when using native format to store image. */
/* set true if unscaled image can be always displayed even when there isn't
* enough memory for resized image. e.g. when using native format to store
* image. */
const bool unscaled_avail;
/* return needed size of buffer to store downscaled image by ds */
/* return needed size of buffer to store downscaled image by ds.
* this is used to calculate min downscale. */
int (*img_mem)(int ds);
/* load image from filename. set width and height of info properly. also, set
* buf_size to remaining size of buf after load image. it is used to caluclate
* min downscale. */
/* load image from filename. use the passed buffer to store loaded, decoded
* or resized image later, so save it to local variables if needed.
* set width and height of info properly. also, set buf_size to remaining
* size of buf after load image. it is used to calculate min downscale.
* return PLUGIN_ERROR for error. ui will skip to next image. */
int (*load_image)(char *filename, struct image_info *info,
unsigned char *buf, ssize_t *buf_size);
/* downscale loaded image by ds. note that buf to store reszied image is not
* provided. return PLUGIN_ERROR for error. ui will skip to next image. */
/* downscale loaded image by ds. use the buffer passed to load_image to
* reszie image and/or store resized image.
* return PLUGIN_ERROR for error. ui will skip to next image. */
int (*get_image)(struct image_info *info, int ds);
/* draw part of image */
void (*draw_image_rect)(struct image_info *info,