tahoma2d/doc/rendering_overview.md

Rendering in Tahoma2D

Understanding the rendering code can be challenging in Tahoma2D

When a render, fast render, or preview command is given, it is handled in rendercommand.cpp

In rendercommand.cpp:

• The file destination is verified.
• The output or preview settings are retrieved
• The scene background color is adjusted if the exported file type does not support transparency.
• The fx stack for each frame is retrieved, including adding an additional over fx to lay the frame over the background color.
• The process is then handed off to a movierenderer or a multimediarenderer.

A movierenderer exports standard image sequences or video formats. (movierenderer.cpp)

A multimediarenderer exports each layer of a frame individually for compositing elsewhere later. (multimediarenderer.cpp)

This document will focus on what happens with a movierenderer.

In movierenderer.cpp:

• A movierenderer class receives the settings from the rendercommand
• This class receives the list of frames to be rendered with their fx stack
• Passes this information on to an Imp class which subclasses TrenderPort
  • The Imp communicates with the renderer and handles post rendering tasks, such as sending rendered frames to the level writer, creating the soundtrack, and adding a clapper board.
• The Imp deletes old files if needed.
• The Imp sets the output size based on the shrink setting from the output settings.
• The Imp set up the Level Updater and Writer which will handled the frames when rendering is done.
• Once all setup is done, the movierenderer calls startRendering.

The process is then handed off to trenderer.cpp

The TRenderer assigns a render id and tells the TRendererStartInvoker to emit start render.

A TRendererStartInvoker is a middle class that emits a startRender message to itself(?) and tells the renderer to begin (startRendering()).

In TRendererImp::startRendering():

• The output area is setup
• An Individual RenderTask is setup for each frame
• The render tasks are launched

RenderTask::run() is where the frame renders begin.

• An empty raster tile is retrieved
• The time is computed in compute()
  • Compute is handled by TRasterFx::compute() - see below
• A notification that the frame is complete is sent

in TRasterFx::compute()

• The tile is adjusted to make sure that it is not at a fractional position
• An alias string is built which contains the fx stack and parameters.
• The tile and relevant info is then passed to a ResourceBuilder

The ResourceBuilder:

• runs build
• checks to see if the resource already exists
• if it doesn't compute() is called
• Compute calls doCompute on the fx
• This fx will call compute on any needed info it needs to do it's processing.
• This can continue for as many fx need info/data.
• Once all fx for a frame have been processed, a final tile should be created and passed back.

The MovieRenderer::Imp will then get the final frames and tell the level writer to save them.