Using renderer.render and composer.render together

Questions
1

Is it possible to call renderer.render to render a scene and then call composer.render to render additional scenes?

Example:

renderPass.clear = false;
composer.addPass( renderPass );
composer.addPass( outlinePass );
composer.addPass( fxaaPass );

renderer.clear();
renderer.render(gridScene, camera);
composer.render();

The outline pass seems to throw away the previous render.
The reason I want to do this is so I can avoid running fxaa and gamma correction on some of the scenes.

2

Well, basically it is possible but only if the pass renders “on top” on the existing framebuffer data (so it does not perform a clear). If you need this behavior for OutlinePass, you have to change the implementations according to your needs.