Rendering only parts of the scene

This snippet requires my RenderTarget from https://github.com/tobspr/RenderTarget, just put it into the same folder.

It shows how to only display parts of the scene, using an arbitrary object as mask (In this case a quad).
Looks like this: http://prntscr.com/9xafvh (Quad is animated)

main.py:

from panda3d.core import *
from RenderTarget import RenderTarget

load_prc_file_data("", """
textures-power-2 none
win-size 1600 900
win-fixed-size #t
""")
import direct.directbase.DirectStart


# Just load the scene, nothing special
scene = loader.loadModel("environment")
scene.reparent_to(base.render)
base.disableMouse()
base.camera.set_pos(30, 30, 30)
base.camera.look_at(0, 0, 20)
base.camLens.set_fov(110)

# Render the scene to a FBO
scene_target = RenderTarget("RenderScene")
scene_target.add_color_texture()
scene_target.prepare_scene_render()

# Create a quad which is our background
cm = CardMaker("cm")
cm.set_frame_fullscreen_quad()
cm.set_color(0.2, 0.6, 1.0, 1.0)
cm_n = cm.generate()
cm_np = render2d.attach_new_node(cm_n)

# Create an arbitrary object (in this case a quad) which shows the scene
quad = CardMaker("cm")
quad.set_frame(-2.0, 2.0, 2.0, -2.0)
quad_n = quad.generate()
quad_np = aspect2d.attach_new_node(quad_n)

# Rotate the panda
quad_np.hprScaleInterval(2.0, Vec3(0, 0, 360), Vec3(0.0)).loop()

# Create a super simple vertex shader, which does not really do anything
vshader = """
#version 400
in vec4 p3d_Vertex;
uniform mat4 p3d_ModelViewProjectionMatrix;
void main() {
    gl_Position = p3d_ModelViewProjectionMatrix * p3d_Vertex;
}
"""

# Create a fragment shader which just displays the texture
fshader = """
#version 400
uniform sampler2D SceneTex;
out vec4 color;
void main() {color = texelFetch(SceneTex, ivec2(gl_FragCoord.xy), 0); }
"""
quad_np.set_shader(Shader.make(Shader.SL_GLSL, vshader, fshader))
quad_np.set_shader_input("SceneTex", scene_target["color"])

base.run()

Cool! The fun thing is that I recently saw a video from the Budget Cuts game (https://www.youtube.com/watch?v=gbp7xX9QPOc) and tough that the ‘‘portal’’ effect looked quite nice.

Out of curiosity, could this effect be achieved with a derivative of this snippet or is there any other way to achieve this effect in panda3D?

Only asking, no (current) intention on working on something like that

Good work!

Everything is possible in panda, its just a matter of how much effort it takes

From what I can see in the video, they are mixing up two different scenes. Basically you would have your main render scene, and you would have a second scene which you render to a FBO. You would then texture your 2D object (in their case, a blue circle) with your second scene to achieve this kind of blending effect.

The snippet currently cannot do that, one would have to extend it with a secondary rendered scene.

You can implement portals using stencils, without render-to-texture. Draw the main scene including the portal disc (which you write to the stencil buffer), and then have a second DisplayRegion layered on top that that renders the other scene, drawing using the stencil test enabled.

Haha ok cool! I am not near good enough with panda3d to try this yet, but that sound like an interesting thing to try eventually!