Transparency is not respected when rendering PDFs

[benj2240]

https://github.com/jhabjan/Ghostscript.NET/blob/49a233f888eff8d3ac67786a602c5fe40b0da675/Ghostscript.NET/Viewer/FormatHandlers/GhostscriptViewerPdfFormatHandler.cs#L274

This line causes incorrect handling of PDFs with embedded transparent images.

Code that determines whether transparency is required on a given page is included in the procedure pdfshowpage_setpage. I'm not clear on what else that procedure does, but the rest of it might be important too.

Unless there is a specific reason that pdfshowpage_setpage is being omitted, it should be included here. Alternatively, this line could be simplified to

this.Execute("Page pdfshowpage");

... which calls pdfshowpage_init, pdfshowpage_setpage, and pdfshowpage_finish in succession (and has done so since at least 2007 for Ghostscript 8.56, and likely earlier).

Attached is an example of a PDF with a transparent image. Currently it is displayed as a black box on a gray background. It should be displayed as the word "hello", in black text on a gray background.

hellopng.pdf

[jhabjan]

Good finding, thanks. I will include this in next release.

[zhjmao]

by using `

this.Execute("Page pdfshowpage");

` transparent image works fine

[jhabjan]

Fixed in today's v.1.2.2. release.