Avoid creation of unnecessary image bufs (at alt-text to img switch)

This is the first of a patch series for image code bugs that have
severe impact on performance.

With these testing files:

1imgA.html  =  <img src="maj00s.png" alt="img1">
2imgSA.html  = <img src="maj00s.png" alt="img1">
               <img src="maj00s.png" alt="img12">
3imgSA.html  = <img src="maj00s.png" alt="img1">
               <img src="maj00s.png" alt="img12">
               <img src="maj00s.png" alt="img123">

2imgA.html  =  <img src="maj00s.png" alt="img1">
               <img src="maj21s.png" alt="img12">
3imgA.html  =  <img src="maj00s.png" alt="img1">
               <img src="maj21s.png" alt="img12">
               <img src="c10s.png" alt="img123">

This are the results:

.------------------------------------------------------------------.
|imgbufs     |         No patch         |         Patched #1       |
|            | first time | upon reload | first time | upon reload |
|-------------------------------------------------------------------
|1imgA.html  |     2      |     1       |     1      |      1      |
|2imgSA.html |     3      |     2       |     1      |      2      |
|3imgSA.html |     4      |     3       |     1      |      3      |
|-------------------------------------------------------------------
|2imgA.html  |     4      |     2       |     2      |      2      |
|3imgA.html  |     6      |     3       |     3      |      3      |
'------------------------------------------------------------------'

1 files changed, 6 insertions, 4 deletions

diff --git a/dw/fltkimgbuf.cc b/dw/fltkimgbuf.cc
index 26b46969..01bce455 100644
--- a/dw/fltkimgbuf.cc
+++ b/dw/fltkimgbuf.cc
@@ -80,7 +80,7 @@ FltkImgbuf::FltkImgbuf (Type type, int width, int height, double gamma)
 {
    DBG_OBJ_CREATE ("dw::fltk::FltkImgbuf");
 
-   _MSG("FltkImgbuf: new root %p\n", this);
+   _MSG ("FltkImgbuf::FltkImgbuf: new root %p\n", this);
    init (type, width, height, gamma, NULL);
 }
 
@@ -89,7 +89,7 @@ FltkImgbuf::FltkImgbuf (Type type, int width, int height, double gamma,
 {
    DBG_OBJ_CREATE ("dw::fltk::FltkImgbuf");
 
-   _MSG("FltkImgbuf: new scaled %p, root is %p\n", this, root);
+   _MSG ("FltkImgbuf::FltkImgbuf: new scaled %p, root is %p\n", this, root);
    init (type, width, height, gamma, root);
 }
 
@@ -135,8 +135,8 @@ void FltkImgbuf::init (Type type, int width, int height, double gamma,
       case RGB:  bpp = 3; break;
       default:   bpp = 1; break;
       }
-      _MSG("FltkImgbuf::init width=%d height=%d bpp=%d gamma=%g\n",
-           width, height, bpp, gamma);
+      _MSG("FltkImgbuf::init this=%p width=%d height=%d bpp=%d gamma=%g\n",
+           this, width, height, bpp, gamma);
       rawdata = new uchar[bpp * width * height];
       // Set light-gray as interim background color.
       memset(rawdata, 222, width*height*bpp);
@@ -163,6 +163,8 @@ void FltkImgbuf::init (Type type, int width, int height, double gamma,
 
 FltkImgbuf::~FltkImgbuf ()
 {
+   _MSG ("FltkImgbuf::~FltkImgbuf\n");
+
    if (!isRoot())
       root->detachScaledBuf (this);