improve read from broken rigol scopes

[rigol] / png.c

diff --git a/png.c b/png.c
index 7606f2bb5f7868895b96fd811f242f9824f175a5..ac09767fb8597d11b910a22db48b3a5dcf804319 100644 (file)
--- a/png.c
+++ b/png.c
@@ -68,7 +68,7 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
        unsigned char lut[256][3];
        unsigned char *screen_deflated;
        int deflated_size;
-       unsigned char *image;
+       unsigned char *image = NULL;
        unsigned char *outpos;
        static const unsigned char png[] = {137, 80, 78, 71, 13, 10, 26, 10};
        static unsigned char idat[] = {'I', 'D', 'A', 'T'};
@@ -117,6 +117,7 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
        strm.next_in = screen_conv;
 
        toalloc = 0;
+       strm.avail_out = 0;
        screen_deflated = NULL;
        flush = Z_NO_FLUSH;
 
@@ -147,7 +148,6 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
 
        deflateEnd(&strm);
 
-
        image = malloc(sizeof(png) +
                sizeof(ihdr) + 8 + /* 8 = length, csum */
                sizeof(idat) + deflated_size + 8 +
@@ -155,12 +155,16 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
        
        if (image == NULL) {
                perror("malloc");
+               return NULL;
        }
        
        outpos = image;
+
+       /* PNG signature */
        memcpy(outpos, png, sizeof(png));
        outpos += sizeof(png);
 
+       /* IHDR */
        l = htonl(sizeof(ihdr) - 4); /* "IHDR" is not counted */
        memcpy(outpos, &l, sizeof(l));
        outpos += sizeof(l);
@@ -170,6 +174,7 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
        memcpy(outpos, &l, sizeof(l));
        outpos += sizeof(l);
 
+       /* IDAT */
        l = htonl(deflated_size);
        memcpy(outpos, &l, sizeof(l));
        outpos += sizeof(l);
@@ -182,6 +187,7 @@ unsigned char *lcd2png(unsigned char *lcd, int *len)
        memcpy(outpos, &l, sizeof(l));
        outpos += sizeof(l);
 
+       /* IEND */
        l = htonl(sizeof(iend) - 4); /* "IEND" is not counted */
        memcpy(outpos, &l, sizeof(l));
        outpos += sizeof(l);