Cannot pass current result to the next rendering - three.js

Question

I am trying to do a progressive rendering using the previous rendering as a texture to the next one.
EDIT 1: As suggested in the comments, I did updated my version of THREE.js to the latest available, and kept my old code, the result is the same (even if the vertical positions of objects flipped). And my problem still remains. Please do consider my update and my pray for help.
Original message:
My fragment shader should only increment the color on the green channel with 0.1, like this:
#ifdef GL_ES
precision highp float;
#endif
uniform sampler2D sampa;
varying vec2 tc;
void main(void)
{
vec4 c = texture2D(sampa, tc);
vec4 t = vec4(c.x, c.y + .1, c.z, 1.);
gl_FragColor = t;
}
My composer is like this:
composer.addPass(renderModel);
composer.addPass(screenPass);
composer.addPass(feedPass);
Where renderModel is a RenderPass, rendering my scene in which I have a plane and a cube.
and screenPass and feedPass are identical with the only difference being that one renders on screen the other one renders in writeBuffer (composer.renderTarget1).
var renderModel = new THREE.RenderPass(scene, camera);
renderModel.clear = false;
screenPass = new THREE.ShaderPass(shader2, 'sampa');
screenPass.renderToScreen = true;
screenPass.clear = false;
screenPass.needsSwap = false;
feedPass = new THREE.ShaderPass(shader2, 'sampa');
feedPass.renderToScreen = false;
feedPass.clear = false;
feedPass.needsSwap = false;
And in the animation loop, I have something like this:
composer.render();
if(step % 250 == 0)
{
newmat = new THREE.MeshBasicMaterial(
{
map : composer.renderTarget1
});
plane.material = newmat;
}
step++;
requestAnimationFrame(animate);
The part with step % 250 is to delay the change of material.
Anyway, the problem is that the plane is disappearing when that happens. Even if it is correctly rendered in the first 250 steps. I guess it is still there but with no texture data, so it is not actually rendered.
I know that EffectComposer is not part of the library, and it is found only in examples, and might not be supported, but I would really do with any advice on this situation, and any answer will be greatly appreciated.
As for any other info about the problem, or some other code that might help I very am willing to share.
Could you point out what am I doing wrong?
I thank you for your kindness.

Answer 1

It seems the solution to this problem is to use two RenderTargets, and switch between them on every step. My limited knowledge stops me from understanding exactly why but this is exactly how EffectComposer work.
For those who might have this problem and need a solution you should try to set needsSwap to true for your shaders pass.
And if you do not use EffectComposer, then remember to use two rendertargets.