jpeg: provide a rough estimate of decoder memory overhead

JPEG decoding requires additional space in the bitmap buffer beyond
what is needed for the decoded pixel data. Provide a way to estimate
how much overhead is needed.

The actual overhead is sizeof(struct jpeg) + decode_buf_size, where
the latter depends on the image size and JPEG encoding used. From my
testing decode_buf_size is normally pretty small (under 5 KiB) but
looking at the code it could be large in some cases, primarily with
large images, so 32 KiB seems to be a decent compromise. Someone who
knows better about JPEG should pick a better value if that's too big.

Using a constant is obviously not the most accurate but it seems to
be the simplest option for retrofitting to existing code.

Change-Id: I573b0abb8ca2d79e43f185010487f07226edb793

1 files changed, 11 insertions, 0 deletions

diff --git a/apps/recorder/jpeg_load.c b/apps/recorder/jpeg_load.c
index 9ab42b7a9f..5b287aff75 100644
--- a/apps/recorder/jpeg_load.c
+++ b/apps/recorder/jpeg_load.c
@@ -2228,4 +2228,15 @@ int read_jpeg_fd(int fd,
 }
 #endif
 
+const size_t JPEG_DECODE_OVERHEAD =
+    /* Reserve an arbitrary amount for the decode buffer
+     * FIXME: Somebody who knows what they're doing should look at this */
+    (32 * 1024)
+#ifndef JPEG_FROM_MEM
+    /* Unless the struct jpeg is defined statically, we need to allocate
+     * it in the bitmap buffer as well */
+    + sizeof(struct jpeg)
+#endif
+    ;
+
 /**************** end JPEG code ********************/