lbximg: Improve performance of PAM output.

The PAM output currently calls fwrite for every pixel, which amounts to
about half a million fwrite calls to output a full screen image.  For a
fullscreen animation like logo.lbx.001, the majority of the execution
time is spent in fwrite.

Let's reduce this a lot by formatting and outputting an entire row at
a time, which almost completely eliminates fwrite from the profile.

diff --git a/src/pnm.c b/src/pnm.c
index d70d8b5ceadf63107d5d4e3fb718e854db17b1f1..1596c5a1e85114bfc12e631f429ea2ef46bbbb7e 100644 (file)
--- a/src/pnm.c
+++ b/src/pnm.c
@@ -322,58 +322,61 @@ int img_output_pam(FILE *f, const char *filename,
                    struct lbx_colour *palette)
 {
        bool masked = img_is_masked(mask, width, height);
-       unsigned x, y, depth;
+       unsigned x, y, depth, maxval = palette ? 63 : 255;
+       unsigned char *rowbuf;
+       int rc;
 
-       if (fprintf_ascii(f, "P7\nWIDTH %u\nHEIGHT %u\n", width, height) < 0)
-               goto err;
+       depth = (palette ? 3 : 1) + masked;
+       if (width > (size_t)-1 / depth || !(rowbuf = malloc(width * depth))) {
+               tool_err(-1, "failed to allocate memory");
+               return -1;
+       }
 
-       if (palette) {
-               depth = masked ? 4 : 3;
+       rc = fprintf_ascii(f, "P7\nWIDTH %u\nHEIGHT %u\nDEPTH %u\n",
+                             width, height, depth);
+       if (rc < 0)
+               goto write_err;
 
-               if (fprintf_ascii(f, "DEPTH %u\nMAXVAL 63\n"
-                                    "TUPLTYPE RGB%s\nENDHDR\n",
-                                    depth, masked ? "_ALPHA" : "") < 0)
-                       goto err;
+       rc = fprintf_ascii(f, "MAXVAL %u\nTUPLTYPE %s",
+                             maxval, palette ? "RGB" : "GRAYSCALE");
+       if (rc < 0)
+               goto write_err;
 
-               for (x = y = 0; y < height; ++x < width || (x = 0, y++)) {
-                       unsigned long offset = (unsigned long) y * width + x;
-                       struct lbx_colour *c = &palette[pixels[offset]];
-                       unsigned char buf[4];
-                       bool vis;
-
-                       vis = mask[offset/CHAR_BIT] & (1u << offset%CHAR_BIT);
-                       buf[0] = c->red;
-                       buf[1] = c->green;
-                       buf[2] = c->blue;
-                       buf[3] = vis ? 63 : 0;
-
-                       if (fwrite(buf, 1, depth, f) < depth)
-                               goto err;
-               }
-       } else {
-               depth = masked ? 2 : 1;
+       rc = fprintf_ascii(f, "_ALPHA\nENDHDR\n" + 6*!masked);
+       if (rc < 0)
+               goto write_err;
 
-               if (fprintf_ascii(f, "DEPTH %u\nMAXVAL 255\n"
-                                    "TUPLTYPE GRAYSCALE%s\nENDHDR\n",
-                                    depth, masked ? "_ALPHA" : "") < 0)
-                       goto err;
-
-               for (x = y = 0; y < height; ++x < width || (x = 0, y++)) {
+       for (y = 0; y < height; y++) {
+               for (x = 0; x < width; x++) {
                        unsigned long offset = (unsigned long) y * width + x;
-                       unsigned char buf[2];
-                       bool vis;
-
-                       vis = mask[offset/CHAR_BIT] & (1u << offset%CHAR_BIT);
-                       buf[0] = pixels[offset];
-                       buf[1] = vis ? 255 : 0;
-
-                       if (fwrite(buf, 1, depth, f) < depth)
-                               goto err;
+                       size_t p = (size_t)depth * x; // pixel start
+
+                       if (palette) {
+                               struct lbx_colour *c = &palette[pixels[offset]];
+                               rowbuf[p+0] = c->red;
+                               rowbuf[p+1] = c->green;
+                               rowbuf[p+2] = c->blue;
+                       } else {
+                               rowbuf[p+0] = pixels[offset];
+                       }
+
+                       if (masked) {
+                               bool vis = 1 & ( mask[offset/CHAR_BIT]
+                                                >> (offset%CHAR_BIT) );
+
+                               rowbuf[p+depth-1] = vis*maxval;
+                       }
                }
+
+               if (fwrite(rowbuf, depth, width, f) < width)
+                       goto write_err;
        }
 
+       free(rowbuf);
        return 0;
-err:
+write_err:
        tool_err(0, "error writing %s", filename);
+
+       free(rowbuf);
        return -1;
 }