GPUOffScreen and draw_texture_2d issues

Coding Python Support
1

I would like to draw to a GPUOffscreen and render its color texture within the view3d editor but dynamically change its size in relation to the view3d.

The size of the GPUOffscreens can’t be changed at runtime so my I’ve attempted to create a new one each time a draw handler is called. For some reason with this approach the offscreen isn’t rendering. Does anybody know why?

I’m using Blender 2.93.2

Example

import bpy
import gpu
import bgl
from gpu_extras.presets import draw_texture_2d


class DynamicOffScreenDrawer():
    def __init__(self):
        self.draw_handle = None
        
    def draw(self):
        print("drawing offscreen")
        context = bpy.context
        scene = context.scene
        w = int(context.area.width / 2)
        h = int(context.area.height / 2)
        offscreen = gpu.types.GPUOffScreen(w, h)
        self.offscreen = offscreen
        view_matrix = scene.camera.matrix_world.inverted()

        projection_matrix = scene.camera.calc_matrix_camera(
            context.evaluated_depsgraph_get(), x=w, y=h)

        offscreen.draw_view3d(
            scene,
            context.view_layer,
            context.space_data,
            context.region,
            view_matrix,
            projection_matrix)

        bgl.glDisable(bgl.GL_DEPTH_TEST)
        draw_texture_2d(offscreen.color_texture, (10, 10), w, h)
        
    def start(self):
        if not self.draw_handle:
            self.draw_handle = bpy.types.SpaceView3D.draw_handler_add(self.draw, (), 'WINDOW', 'POST_PIXEL')
            
    def end(self):
        if self.draw_handle:
            bpy.types.SpaceView3D.draw_handler_remove(self.draw, 'WINDOW')
            self.draw_handle = None
        
        
offscreendrawer = DynamicOffScreenDrawer()
offscreendrawer.start()

for area in bpy.context.screen.areas:
        if area.type == "VIEW_3D":
            for region in area.regions:
                if region.type == "WINDOW":
                    region.tag_redraw()

Example of working offscreen drawing but without resizing in relation to the view3d

import bpy
import gpu
import bgl
from gpu_extras.presets import draw_texture_2d


class OffScreenDrawer():
    def __init__(self, width, height):
        self.draw_handle = None
        self.offscreen = gpu.types.GPUOffScreen(width, height)
        
    def draw(self):
        print("drawing offscreen")
        context = bpy.context
        scene = context.scene
        offscreen = self.offscreen
        
        view_matrix = scene.camera.matrix_world.inverted()

        projection_matrix = scene.camera.calc_matrix_camera(
            context.evaluated_depsgraph_get(), x=offscreen.width, y=offscreen.height)

        offscreen.draw_view3d(
            scene,
            context.view_layer,
            context.space_data,
            context.region,
            view_matrix,
            projection_matrix)

        bgl.glDisable(bgl.GL_DEPTH_TEST)
        draw_texture_2d(offscreen.color_texture, (10, 10), offscreen.width, offscreen.height)
        
    def start(self):
        if not self.draw_handle:
            self.draw_handle = bpy.types.SpaceView3D.draw_handler_add(self.draw, (), 'WINDOW', 'POST_PIXEL')
            
    def end(self):
        if self.draw_handle:
            bpy.types.SpaceView3D.draw_handler_remove(self.draw, 'WINDOW')
            self.draw_handle = None
        
        
offscreendrawer = OffScreenDrawer(256, 256)
offscreendrawer.start()

for area in bpy.context.screen.areas:
        if area.type == "VIEW_3D":
            for region in area.regions:
                if region.type == "WINDOW":
                    region.tag_redraw()

If I run the first example, then run the the second example nothing is drawn also.