render targets

needed to make things like brush strokes? How are brushes in Adobe implemented?

a conversation with ChatGPT

Q: Explain render targets like I am 5 A: Alright! Imagine you’re drawing a picture on a piece of paper. That paper is where all the colors, shapes, and details go. In the world of computers, when we’re making images or games, we use something like that piece of paper called a render target. It’s a special spot where the computer “draws” everything before showing it to you on the screen. So, just like you would need a piece of paper to draw on before showing your picture to someone, the computer uses a render target to “draw” everything that will eventually show up on your screen!

Q: Does that mean render targets and FBOs are the same? A: Render target is a general term for the place where the computer draws the final image, like our “piece of paper” example. It can be the screen or some off-screen space. An FBO is a type of render target that’s off-screen and flexible, used when you need to draw things that aren’t immediately visible but are important for the final image.

Q: Do softwares like Adobe use render targets or FBOs to render brush strokes? A: When you draw a brush stroke, the software doesn’t immediately draw it directly to the final image (your canvas on the screen). Instead, it often uses an off-screen buffer (similar to an FBO) to process the brush stroke. This helps with things like smoothing, blending, and applying effects in real-time. Here’s how it works in a simplified way:

1. Off-screen rendering: The brush stroke is first rendered onto a temporary off-screen surface (like an FBO).
2. Processing: The stroke can be smoothed, adjusted for pressure sensitivity, or have effects like blur or texture applied while in this temporary space.
3. Display: Once the brush stroke is processed, it’s drawn onto the main canvas (the render target) that you see on the screen. This method allows for smooth, responsive drawing without directly affecting the final image until the stroke is ready, and it’s key to making real-time editing efficient in graphics software.

Q: Can you give me a general overview of how to implement this functionality in three.js? reminder to try this later and this → https://blog.maximeheckel.com/posts/beautiful-and-mind-bending-effects-with-webgl-render-targets/ A: In three.js, you can implement off-screen rendering similar to how render targets and FBOs work by using WebGLRenderTarget. This is especially useful when you want to render something off-screen, process it, and then use it as a texture or combine it with other visuals before displaying the final result.

Here’s a general overview of how to implement this:

Steps to Render Brush Strokes Off-Screen in three.js:

1. Set Up Your Scene, Camera, and Renderer

Just like any three.js project, you first set up your main scene, camera, and renderer.

const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth / window.innerHeight, 0.1, 1000);
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
 
camera.position.z = 5;

2. Create a Render Target (Off-Screen Buffer)

To render off-screen, you need a WebGLRenderTarget, which acts like an off-screen canvas or FBO.

const renderTarget = new THREE.WebGLRenderTarget(window.innerWidth, window.innerHeight);

3. Create a Scene for Brush Strokes

Create a separate scene where you will render the brush strokes. This scene will render to the WebGLRenderTarget.

const brushScene = new THREE.Scene();

4. Create a Brush Stroke Object

You can use geometries or custom shaders to create brush strokes. For simplicity, let’s assume you create a basic plane that represents a brush stroke. You can update it with each brush interaction.

const geometry = new THREE.PlaneGeometry(1, 1); // Adjust size for brush stroke
const material = new THREE.MeshBasicMaterial({ color: 0xff0000 }); // Red brush stroke
const brushStroke = new THREE.Mesh(geometry, material);
brushScene.add(brushStroke);

5. Render Brush Strokes to the Render Target

Now, render your brush strokes off-screen. Instead of rendering to the main screen, you render to the WebGLRenderTarget.

renderer.setRenderTarget(renderTarget);
renderer.render(brushScene, camera);
renderer.setRenderTarget(null); // Reset back to default rendering target

6. Apply the Render Target as a Texture

Once the strokes are rendered, you can use the renderTarget as a texture on other objects in your main scene, like the canvas or a display object.

const texture = renderTarget.texture;
const canvasMaterial = new THREE.MeshBasicMaterial({ map: texture });
const canvas = new THREE.Mesh(new THREE.PlaneGeometry(5, 5), canvasMaterial);
scene.add(canvas);

7. Render the Main Scene

Finally, you render the main scene where the processed texture (your brush strokes) is now applied.

function animate() {
    requestAnimationFrame(animate);
    renderer.render(scene, camera);
}
animate();

Summary:

• You set up a WebGLRenderTarget as your off-screen buffer.
• Render brush strokes or any other off-screen content to the brushScene using the off-screen buffer.
• Use the resulting renderTarget.texture as a texture to apply to objects in your main scene.
• Render the main scene to display everything on the screen.

This approach lets you perform complex operations (like brush strokes, post-processing, or effects) without directly modifying the main scene, offering flexibility and smooth performance.