Perspective

perspective.py

# flake8: noqa
"""
Perspective example using the lower level rendering API.

This is definitely in the advanced section, but it can be
a useful tool to learn. Sometimes we want perspective
projection for things like backgrounds. This can be
done very efficiently with shaders.

In this example we render content into a framebuffer /
virtual screen and map that on a texture we can rotate
in 3D.

If Python and Arcade are installed, this example can be run from the command line with:
python -m arcade.examples.perspective
"""

from __future__ import annotations

from array import array

import arcade
from pyglet.math import Mat4
from arcade.gl import BufferDescription


class Perspective(arcade.Window):

    def __init__(self):
        super().__init__(800, 600, "Perspective", resizable=True)
        # Simple texture shader for the plane.
        # It support projection and model matrix
        # and a scroll value for texture coordinates
        self.program = self.ctx.program(
            vertex_shader="""
            #version 330

            uniform mat4 projection;
            uniform mat4 model;

            in vec3 in_pos;
            in vec2 in_uv;

            out vec2 uv;

            void main() {
                gl_Position = projection * model * vec4(in_pos, 1.0);
                uv = in_uv;
            }
            """,
            fragment_shader="""
            #version 330

            uniform sampler2D layer;
            uniform vec2 scroll;

            in vec2 uv;
            out vec4 fragColor;

            void main() {
                fragColor = texture(layer, uv + scroll);
            }
            """,
        )

        # # Matrix for perspective projection
        self.proj = Mat4.perspective_projection(self.aspect_ratio, 0.1, 100, fov=75)
        # # Configure the projection in the shader
        self.program["projection"] = self.proj

        # Framebuffer / virtual screen to render the contents into
        self.fbo = self.ctx.framebuffer(
            color_attachments=self.ctx.texture(size=(1024, 1024))
        )

        # Set up the geometry buffer for the plane.
        # This is four points with texture coordinates
        # creating a rectangle
        buffer = self.ctx.buffer(
            data=array(
                'f',
                [
                    # x  y   z  u  v 
                    -1,  1, 0, 0, 1,  # Top Left     
                    -1, -1, 0, 0, 0,  # Bottom Left
                     1,  1, 0, 1, 1,  # Top Right
                     1, -1, 0, 1, 0,  # Bottom right
                ]
            )
        )
        # Make this into a geometry object we can draw-
        # Here we describe the contents of the buffer so the shader can understand it
        self.geometry = self.ctx.geometry(
            content=[BufferDescription(buffer, "3f 2f", ("in_pos", "in_uv"))],
            mode=self.ctx.TRIANGLE_STRIP,
        )

        # Create some sprites
        self.spritelist = arcade.SpriteList()
        for y in range(8):
            for x in range(8):
                self.spritelist.append(
                    arcade.Sprite(
                        ":resources:images/tiles/boxCrate_double.png",
                        center_x=64 + x * 128,
                        center_y=64 + y * 128,
                    )
                ) 
        self.time = 0

    def on_draw(self):
        # Every frame we can update the offscreen texture if needed
        self.draw_offscreen()
        # Clear the window
        self.clear()

        # Bind the texture containing the offscreen data to channel 0
        self.fbo.color_attachments[0].use(unit=0)

        # Move the plane into camera view and rotate it
        translate = Mat4.from_translation((0, 0, -2))
        rotate = Mat4.from_rotation(self.time / 2, (1, 0, 0))
        self.program["model"] = translate @ rotate

        # Scroll the texture coordinates
        self.program["scroll"] = 0, -self.time / 5

        # Draw the plane
        self.geometry.render(self.program)

    def on_update(self, delta_time: float):
        self.time += delta_time

    def draw_offscreen(self):
        """Render into the texture mapped """
        # Activate the offscreen framebuffer and draw the sprites into it
        with self.fbo.activate() as fbo:
            fbo.clear()
            arcade.set_viewport(0, self.fbo.width, 0, self.fbo.height)
            self.spritelist.draw()

    def on_resize(self, width: int, height: int):
        super().on_resize(width, height)
        self.program["projection"] = Mat4.perspective_projection(self.aspect_ratio, 0.1, 100, fov=75)


Perspective().run()