split out find_aa_density

diff --git a/pctb/structure.c b/pctb/structure.c
index f0de5fa964d05f0c9e135b17fb99965200fff10b..1045d19cac4a567676160c1b7b72d6d8428ede3b 100644 (file)
--- a/pctb/structure.c
+++ b/pctb/structure.c
@@ -464,6 +464,39 @@ void read_screenshots(void) {
   progress_log("read %d screenshots.",npages);
 }
 
+static double find_aa_density(const RgbImage *ri, Point p, long background,
+                             long foreground, int fg_extra) {
+  Rgb here= ri_rgb(ri, p.x, p.y);
+
+  double alpha[3], alpha_mean=0;
+  int i;
+  for (i=0; i<3; i++) {
+    unsigned char here_chan= here       >> (i*8);
+    unsigned char bg_chan=   background >> (i*8);
+    unsigned char fg_chan=   foreground >> (i*8);
+    double alpha_chan=
+      ((double)here_chan    - (double)bg_chan) /
+      ((fg_chan + fg_extra) - (double)bg_chan);
+    alpha[i]= alpha_chan;
+    alpha_mean += alpha_chan * (1/3.0);
+  }
+
+  double thresh= 1.5/AAMAXVAL;
+  double alpha_min= alpha_mean - thresh;
+  double alpha_max= alpha_mean + thresh;
+  for (i=0; i<3; i++)
+    MUST( alpha_min <= alpha[i] && alpha[i] <= alpha_max,
+         MRGB(here);MRGB(background);MRGB(foreground);MI(fg_extra);
+         MF(alpha_min); MI(i);MF(alpha[i]);MF(alpha_max) );
+
+  MUST( 0 <= alpha_mean &&
+       (fg_extra ? alpha_mean < 0.999 : alpha_mean >= 1.0),
+       MRGB(here);MRGB(background);MRGB(foreground);MI(fg_extra);
+       MF(alpha_mean); MF(alpha[0]);MF(alpha[1]);MF(alpha[2]); );
+
+  return alpha_mean;
+}
+
 static void find_commodity(int offset, Rect *rr) {
   /* rr->tl.x==-1 if offset out of range */
   rr->tl.y= commbasey - offset*comminty;
@@ -524,32 +557,9 @@ static void find_table_entry(Rect commod, int colno, Rect *cell) {
   int monochrome= 1;
 
   FOR_P_RECT(p,*cell) {
-    Rgb here= ri_rgb(ri, p.x, p.y);
-    double alpha[3], alpha_mean=0;
-    int i;
-    for (i=0; i<3; i++) {
-      unsigned char here_chan= here       >> (i*8);
-      unsigned char bg_chan=   background >> (i*8);
-      unsigned char fg_chan=   foreground >> (i*8);
-      double alpha_chan=
-       ((double)here_chan    - (double)bg_chan) /
-       ((fg_chan + fg_extra) - (double)bg_chan);
-      alpha[i]= alpha_chan;
-      alpha_mean += alpha_chan * (1/3.0);
-    }
+    double alpha= find_aa_density(ri,p,background,foreground,fg_extra);
 
-    double thresh= 1.5/AAMAXVAL;
-    double alpha_min= alpha_mean - thresh;
-    double alpha_max= alpha_mean + thresh;
-    for (i=0; i<3; i++)
-      MUST( alpha_min <= alpha[i] && alpha[i] <= alpha_max,
-           MI(i);MRGB(here);MRGB(background);MRGB(foreground);
-           MF(alpha_min);MF(alpha[i]);MF(alpha_max) );
-
-    MUST( 0 <= alpha_mean && alpha_mean < 0.999,
-         MRGB(here);MRGB(background);MRGB(foreground);
-         MF(alpha_mean); MF(alpha[0]);MF(alpha[1]);MF(alpha[2]); );
-    int here_int= floor((AAMAXVAL+1)*alpha_mean);
+    int here_int= floor((AAMAXVAL+1)*alpha);
     assert(here_int <= AAMAXVAL);
     if (!(here_int==0 || here_int==AAMAXVAL)) monochrome=0;
     cim->d[p.y * cim->w + p.x]= '0' + here_int;