如何使用Foxit PDF SDK（iOS版）进行渲染

PDF渲染是通过Foxit渲染引擎实现的，Foxit渲染引擎是一个图形引擎，用于将页面渲染到位图或平台设备上下文。 Foxit PDF SDK提供了APIs用来设置渲染选项/flags，例如设置 flag来决定是否渲染表单域和签名，是否绘制图像反锯齿 (anti-aliasing) 和路径反锯齿。可以使用以下APIs进行渲染：

• 渲染页面和注释时，首先使用FSRenderer::setRenderContentFlags接口来决定是否同时渲染页面和注释，然后使用FSRenderer::startRender接口进行渲染。FSRenderer::startQuickRender接口也可以用来渲染页面，但仅用于缩略图。
• 渲染单个annotation注释，使用FSRenderer::renderAnnot接口。
• 在位图上渲染，使用FSRenderer::startRenderBitmap接口。
• 渲染一个重排的页面，使用FSRenderer::startRenderReflowPage 接口。

在Foxit PDF SDK中，Widget注释常与表单域和表单控件相关联。渲染widget注释，推荐使用如下的流程：

• 加载PDF页面后，首先渲染页面以及该页面上所有的注释 (包括widget注释)。
• 然后，如果使用FSFiller对象来填表，则应使用FSFiller::render接口来渲染当前获取到焦点的表单控件，而不是使用FSRenderer::renderAnnot接口。

如何将指定的PDF页面渲染到bitmap

#import "ViewController.h"
#import <FoxitRDK/FSPDFViewControl.h>
...

-(FSBitmap*)renderPageToBitmap:(FSPDFPage*) pdfPage drawWidth:(int)drawPageWidth drawHeight:(int)drawPageHeight
{
    // If the page hasn't been parsed yet, throw an exception.
    if(![pdfPage isParsed])
        @throw [NSException exceptionWithName:NSGenericException reason:@"PDF Page should be parsed first" userInfo:nil];
    
    // Pepare matrix to render on the bitmap.
    FSMatrix2D* matrix = [pdfPage getDisplayMatrix:0 top:0 width:drawPageWidth height:drawPageHeight rotate:FSRotation0];
    // Create a bitmap according to the required drawPageWidth and drawPageHeight.
    FSBitmap* bitmap = [[FSBitmap alloc] initWithWidth:drawPageWidth height:drawPageHeight format:FSBitmapDIBRgb];
    // Fill the bitmap with white color.
    [bitmap fillRect:0xFFFFFFFF rect:nil];
    FSRenderer* renderer = [[FSRenderer alloc] initWithBitmap:bitmap is_rgb_order:YES];
    // Set the render flag, both page content and annotation will be rendered.
    [renderer setRenderContentFlags:FSRendererRenderPage | FSRendererRenderAnnot];
    // Start to render the page progressively.
    FSProgressive* progress = [renderer startRender:pdfPage matrix:matrix pause:nil];
    if(progress) {
        FSProgressiveState state = [progress resume];
        while (state == FSProgressiveToBeContinued) {
            state = [progress resume];
        }
        if(state != FSProgressiveFinished)
            return nil;
    }
    return bitmap;
}

如何将指定的PDF页面渲染到平台设备上下文

#import "ViewController.h"
#import <FoxitRDK/FSPDFViewControl.h>
...

-(void)renderPageToContext:(FSPDFPage*) pdfPage context:(CGContextRef)context
{
    // If the page hasn't been parsed yet, throw an exception.
    if(![pdfPage isParsed])
        @throw [NSException exceptionWithName:NSGenericException reason:@"PDF Page should be parsed first" userInfo:nil];
    
    // We set the width of drawing page to be equal to screen width, the drawing page height is calculated according to the ratio of page height and width.
    CGFloat scale = [UIScreen mainScreen].scale;
    int drawPageWidth = (int)[[UIScreen mainScreen] bounds].size.width * scale;
    float pageWidth = [pdfPage getWidth];
    float pageHeight = [pdfPage getHeight];
    int drawPageHeight = (int)drawPageWidth * (pageHeight/pageWidth) * scale;
    
    // Erase the background of context with white color.
    CGContextSaveGState(context);
    CGContextSetRGBFillColor(context, 1.0, 1.0, 1.0, 1.0);
    CGContextFillRect(context, CGRectMake(0, 0, drawPageWidth, drawPageHeight));
    
    // Render to screen in the device coordinate, left:0, top:0, right:drawPageWidth, bottom:drawPageHeight.
    FSMatrix2D* matrix = [pdfPage getDisplayMatrix:0 top:0 width:drawPageWidth height:drawPageHeight rotate:FSRotation0];
    FSRenderer* renderer = [[FSRenderer alloc] initWithContext:context device_type:FSRendererDeviceDisplay];
    [renderer setRenderContentFlags:FSRendererRenderPage | FSRendererRenderAnnot];
    // Start to render the page progressively.
    FSProgressive* progress = [renderer startRender:pdfPage matrix:matrix pause:nil];
    if(progress) {
        FSProgressiveState state = [progress resume];
        while (state == FSProgressiveToBeContinued) {
            state = [progress resume];
        }
    }
    CGContextRestoreGState(context);    
}