In this section, you’ll learn how to create custom paint and path objects. This enables you to perform custom computed draw commands using the Rive Renderer.

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Overview

The following classes are available:

  • BlendMode: determines how the source pixels are blended with the destination pixels.
  • Color: determines the color of the shape.
  • Gradient: determines the color gradient of the shape (LinearGradient or RadialGradient)
  • Paint: describes how to draw a shape - see Paint.
  • PaintingStyle: determines if the shape is filled or stroked.
  • Path: defines a shape’s outline or a clipping mask - see Path.
  • StrokeCap: determines how the path’s endpoints are drawn.
  • StrokeJoin: the kind of finish to place on the joins between segments.

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RenderQueue

Create a Rive.RenderQueue and a Rive.Renderer:

public RenderTexture renderTexture;
private Rive.RenderQueue m_renderQueue;
private Rive.Renderer m_riveRenderer;

...

m_renderQueue = new RenderQueue(renderTexture);
m_riveRenderer = m_renderQueue.Renderer();

Call draw on the render queue and pass in a Path and Paint object.

m_path = new Path();
m_paint = new Paint();
m_riveRenderer.Draw(m_path, m_paint);

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Path

A path is a series of drawing commands. The path is used to define a shape’s outline or a clipping mask.

Create a new path:

m_path = new Path();

The Path class provides various methods to construct a path:

  • moveTo: Moves the current point to the given point.
  • lineTo: Adds a straight line from the current point to the given point.
  • circle: Adds a circle to the path.
  • cubicTo: Adds a cubic bezier curve to the path.
  • quadTo: Adds a quadratic bezier segment that curves from the current point.
  • addPath: Adds the sub-paths of path to this path, transformed by the provided matrix.
  • close: Closes the path. This will draw a line from the current point to the first point in the path.
  • reset: Resets the path to an empty state.
  • flush: to flush the path to native memory.

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Paint

Paint is used to describe how to draw a shape.

Create a new paint:

m_paint = new Paint();

The paint describes the color, gradient, style, thickness, blend mode, stroke cap, and stroke join for a shape.

Call .Flush() to flush the paint to native memory. See the Example below.

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Example

This example demonstrates drawing an animated triangle to a RenderTexture.

Rive Unity: Procedural Rendering

The MonoBehaviour to create the above:

using System.Collections;
using UnityEngine;
using UnityEngine.Rendering;
using UnityEditor;
using Rive;

public class RiveProcedural : MonoBehaviour
{
    public RenderTexture renderTexture;
    private Rive.RenderQueue m_renderQueue;
    private Rive.Renderer m_riveRenderer;
    private CommandBuffer m_commandBuffer;

    private Camera m_camera;

    Path m_path;
    Paint m_paint;
    private void Start()
    {
        m_renderQueue = new RenderQueue(renderTexture);
        m_riveRenderer = m_renderQueue.Renderer();
        m_path = new Path();
        m_paint = new Paint();
        m_paint.Color = new Rive.Color(0xFFFF0000);
        m_paint.Style = PaintingStyle.stroke;
        m_paint.Join = StrokeJoin.round;
        m_paint.Thickness = 20.0f;
        m_riveRenderer.Draw(m_path, m_paint);

        m_commandBuffer = new CommandBuffer();
        m_commandBuffer.SetRenderTarget(renderTexture);
        m_riveRenderer.AddToCommandBuffer(m_commandBuffer);
        m_camera = Camera.main;
        if (m_camera != null)
        {
            Camera.main.AddCommandBuffer(CameraEvent.AfterEverything, m_commandBuffer);
        }
    }


    private void Update()
    {
        if (m_path == null)
        {
            return;
        }
        m_path.Reset();

        float expand = Time.fixedTime * 10;
        m_path.MoveTo(256, 256 - 100 - expand);
        m_path.LineTo(256 + 50 + expand, 256 + 50 + expand);
        m_path.LineTo(256 - 50 - expand, 256 + 50 + expand);
        m_path.Close();
        m_path.Flush();


        m_paint.Thickness = (Mathf.Sin(Time.fixedTime * Mathf.PI * 2) + 1.0f) * 20.0f + 1.0f;
        m_paint.Flush();
    }

    private void OnDisable()
    {
        if (m_camera != null && m_commandBuffer != null)
        {
            m_camera.RemoveCommandBuffer(CameraEvent.AfterEverything, m_commandBuffer);
        }
    }
}

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Additional Resources

See the getting-started project in the examples repository for a complete example and open the ProceduralRenderingScene scene.