Monkeybread Software - DynaPDF Manual

DynaPDF Manual - Page 670

Function Reference

Page 670 of 860

The zoom factor should take the page format into account and not simply multiply the device

coordinates with a specific factor. The zoom factor must be restricted so that no number overflow

occurs. A suitable limit is around 32 or 64 (6400%).

The OnUpdateWindow Event

When rendering complex PDF pages in a viewer it is strongly recommended to update the window

from time to time with the portion of contents that was already rendered. To achieve this, the

structure TPDFRasterImage supports two variables which specify when the window should be

updated as well as a corresponding callback function that is executed if one of the limits were

reached.

Please note that when the TOnUpdateWindow callback function is set, it is not required to draw

the image into the window after RenderPage() was called!

When the callback function is set, RenderPage() fires at least one update event that covers the entire

imageble area. In the best case, the page was already fully rendered at this point. Calling

SetDIBitsToDevice() or similar system functions after RenderPage() is not required and causes just

unnecessary overhead!

This behaviour can be adjusted if necessary with the flags SKIP_INI_SCREEN, and

SKIP_UPDATE_SCREEN. These flags can be combined with the member StructSize of the

TPDFRasterImage structur as follows:

TPDFRasterImage img;

img.StructSize = sizeof(img) | SKIP_INIT_SCREEN | SKIP_UPDATE_SCREEN.

As the name suggessts the flag SKIP_INIT_SCREEN omits the initial screen initialisation before

rendering starts. SKIP_UPDATE_SCREEN disables the final update screen event after the page was

fully rendered.

The update area

The callback function returns the area that must be updated. It is strongly recommended to update

only this area. This can drastically speed up processing and the application can process more update

events with less overhead. The first call covers the entire imageble area when InitWhite or

DrawFrameRect was set to true. Further calls occur only when the page was not already fully

rendered at this point.

UpdateOnPathCount limit

The member UpdateOnPathCount specifies the number of paths which must be drawn before the

callback function should be executed. The value should not be too small to avoid too many update

events. When the value is too large then too few update events occur and you cannot see how the

page is drawn.

The test containers use a limit of 5000. This is a good compromise between speed and the number of

update events on faster computer systems. DynaPDF counts also the number of vertices which were