Add simple scroll of long waveform

_web_server/server/index.html

@@ -119,6 +119,11 @@
               width: 50%;
               height: 100%;
           }
+
+          #logdiv pre {
+              position: absolute;
+              height: 100%;
+          }
       }
     </style>
   </head>

_web_server/server/playground-server.scm

@@ -744,12 +744,22 @@
 ;;;
 ;;; Make log HTML
 ;;;
-(define (make-log-html log vcd canvas-width)
+(define* (make-log-html log vcd canvas-width #:key
+                        (minimum-sample-width 10)
+                        (maximum-canvas-width 20000))
   (if vcd
-      (format "~a<br/>\n<pre id=\"log\">~a</pre>\n"
-              (string-concatenate
-               (vcd->svg vcd canvas-width))
-              log)
+      (let ((need-width
+             (* minimum-sample-width
+                (length (vcd-timestamps vcd)))))
+        (format "~a<br/>\n<pre id=\"log\">~a</pre>\n"
+                (string-concatenate
+                 (vcd->svg vcd
+                           (if (< need-width canvas-width)
+                               canvas-width
+                               (if (> need-width maximum-canvas-width)
+                                   maximum-canvas-width
+                                   need-width))))
+                log))
       (format "<pre>~a</pre>\n" log)))
 
 ;;;