Allow context to be refreshed after rendering

lib/postproc/canvas.js

@@ -31,9 +31,6 @@ class CanvasRenderer extends Postprocessor{
  this.slant = 0;
  this.sourceFile = "";
  this.tm = null;
- this.word = "";
- this.wordX = 0;
- this.wordY = 0;
  this.x = 0;
  this.y = 0;
  this.zoom = 1;
@@ -138,8 +135,11 @@ class CanvasRenderer extends Postprocessor{
 
 
 
- renderPage(pageIndex, context){
- this.context = context;
+ renderPage(pageIndex, context = null, clear = true){
+ if(null !== context)
+ this.context = context;
+ if(clear)
+ this.clearPage();
 
  // Cap index to available page range
  const max = this.pages.length - 1;
@@ -150,7 +150,7 @@ class CanvasRenderer extends Postprocessor{
  this.page = this.pages[pageIndex];
 
  const aspectRatio = this.pageHeight / this.pageWidth;
- const {canvas} = context;
+ const {canvas} = this.context;
  canvas.height = canvas.width * aspectRatio;
 
  for(const [type, data] of this.page){
@@ -163,6 +163,12 @@ class CanvasRenderer extends Postprocessor{
  }
 
 
+ clearPage(){
+ const {canvas} = this.context;
+ this.context.clearRect(0, 0, canvas.width, canvas.height);
+ }
+
+
  drawArc(args){
  const h0 = this.x * this.scale;
  const v0 = this.y * this.scale;