WebAPI/WebPrintAPI

First iteration: WebPrintAPI

Scope

This is about implementing a new API for printing on the web. It's a "low level" API that allows web developers to have rich control about printing output.

Proposed API

• Use points as metric for printing (72 points per inch)
• Open Questions
  • Should the developer set the page size or should the page size be set by choosing a printer and then using the printer's paper size setup?
  • What is (0,0)? The top left corner of the physical page OR of the page taking into account the print margin?
  • Should there be different color spaces then RGB? How to make them work, as there are no CSS colors defined for CMYK.
  • Lot more... TBD

 var pDoc = new PrintDocument(
                 'documentTitle',  // Title
                 'letter',         // Paper size
                 false             // optional: isLandscape?
                 );
 
 // ---
 // Following things MUST be defined/set by the developer.
 // ---
 
 // The number of pages to print.
 pDoc.calcPageCount = function(fontCtx) {
   var pageCount;
   
   // ..
 
   // The fontCtx is only a very limited subset of the normal print ctx, that
   // basically allows to do font-size measurements.
   fontCtx.font = '...';
   fontCtx.measureText(...);
   
   //...
   
   return pageCount; // 42
 };
 
 // Actually drawing function. Each page is painted individually. This is
 // handy for page preview or if the user picks only a subset of the total
 // pages.
 pDoc.renderPage = function(pageNumber, ctx) {
   if (ctx.isPreview) {
     var dpi = ctx.DPI;
     
     // Only draw images in low resolution for preview
     // ...
   }
   
   
   // Render the page <pageNumber> to the ctx.
   ctx.draw...
   // ...
   
   // If the drawing takes very long, the developer might want to use
   // setTimeouts and continue the painting later one.
   if (printingTakesLong()) {
     setTimeout(function() {
       // Continue drawing...
    
       // This page is done drawing.
       ctx.endPage();
     })
   } else {
     ctx.endPage();
   }
 }
 
 // ---
 // Other APIs
 // ---
 pDoc.getPageSize = function() {
   return {
     width:  <widthInInch>,
     height: <heightInInch>,
   }
 }
 
 pDoc.isPrinting;
 
 // Start the printing progress. This opens the print dialog.
 pDoc.print();
 
 pDoc.abort();

Implementation

None.