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Unity Engine

User Manual

Script Reference

Unity Engine

Generate 2D visual content

Understand the Mesh API, the Vector API, and the types of graphics that you can create with the Vector API.
阅读时间6 分钟最后更新于 1 个月前
You can use the Mesh API or Painter2D to generate 2D visual content onto a visual element.
You can use the Mesh API to draws custom shapes. The Mesh API is a tool for advanced users. If you only want to generate simple geometry, use the Vector API instead. Inspired by HTML Canvas, the Vector API draws 2D vector graphics, such as lines, arcs, and shapes.

Use the Mesh API

To use the Mesh API, allocate a mesh with the 
MeshGenerationContext.Allocate
 method and then fill the vertices and indices. The 
MeshGenerationContext.Allocate
 method allocates and draws the specified number of vertices and indices required to express geometry for drawing the content of a visual element. For details on geometry generation conventions, see Vertex.position.
The following code snippet generates a single quad. It allocates vertices and indices, and provides coordinates in a clockwise direction:
class QuadMeshElement : VisualElement{    public Color color = Color.red;    public QuadMeshElement()    {        generateVisualContent += OnGenerateVisualContent;    }    void OnGenerateVisualContent(MeshGenerationContext mgc)    {        var mesh = mgc.Allocate(4, 6);        var p0 = Vector2.zero;        var p1 = new Vector2(layout.width, 0);        var p2 = new Vector2(layout.width, layout.height);        var p3 = new Vector2(0, layout.height);        mesh.SetNextVertex(new Vertex() { position = new Vector3(p0.x, p0.y, Vertex.nearZ), tint = color });        mesh.SetNextVertex(new Vertex() { position = new Vector3(p1.x, p1.y, Vertex.nearZ), tint = color });        mesh.SetNextVertex(new Vertex() { position = new Vector3(p2.x, p2.y, Vertex.nearZ), tint = color });        mesh.SetNextVertex(new Vertex() { position = new Vector3(p3.x, p3.y, Vertex.nearZ), tint = color });        mesh.SetNextIndex(0);        mesh.SetNextIndex(1);        mesh.SetNextIndex(2);        mesh.SetNextIndex(0);        mesh.SetNextIndex(2);        mesh.SetNextIndex(3);    }}

Use the Painter2D API

To use the Painter2D API, access the 
Painter2D
 object from the 
MeshGenerationContext
 and generate paths with it. You can then use 
Stroke
 to draw lines or 
Fill
 to draw shapes.
To build paths, you issue commands that move a kind of "virtual pen." For example, to generate the same quad in the Mesh API example, move the "pen" to the first position, and chain lines together. After the path is done, use 
Fill
 to build the shape.
class QuadVectorElement : VisualElement{    public Color color = Color.red;    public QuadVectorElement()    {        generateVisualContent += OnGenerateVisualContent;    }    void OnGenerateVisualContent(MeshGenerationContext mgc)    {        var p0 = Vector2.zero;        var p1 = new Vector2(layout.width, 0);        var p2 = new Vector2(layout.width, layout.height);        var p3 = new Vector2(0, layout.height);        var painter2D = mgc.painter2D;        painter2D.fillColor = color;        painter2D.BeginPath();        painter2D.MoveTo(p0);        painter2D.LineTo(p1);        painter2D.LineTo(p2);        painter2D.LineTo(p3);        painter2D.ClosePath();        painter2D.Fill();    }}

Line

The 
LineTo
 method generates a straight line from the current pen position to the provided one. Before you draw lines, define properties, such as the stroke color, the line width, the joins, and caps.
When you draw lines, the properties of 
LineJoin
 and 
LineCap
 control the styles of line joins and caps.
The following image illustrates the different styles of line caps and joins:

Different styles of line caps and joins

The following code snippet draws a zigzag line:

A zigzag line

painter2D.lineWidth = 10.0f;painter2D.strokeColor = Color.white;painter2D.lineJoin = LineJoin.Round;painter2D.lineCap = LineCap.Round;painter2D.BeginPath();painter2D.MoveTo(new Vector2(100, 100));painter2D.LineTo(new Vector2(120, 120));painter2D.LineTo(new Vector2(140, 100));painter2D.LineTo(new Vector2(160, 120));painter2D.LineTo(new Vector2(180, 100));painter2D.LineTo(new Vector2(200, 120));painter2D.LineTo(new Vector2(220, 100));painter2D.Stroke();

Arc

You can use the following methods to draw arcs:
  • The 
    Arc
     method generates an arc from the provided arc center, the radius, and the starting and ending angles.
  • The 
    ArcTo
     method generates an arc between two straight segments.
The following code snippet uses 
Arc
to draws a sector with a border:

A sector with a border

painter2D.lineWidth = 2.0f;painter2D.strokeColor = Color.red;painter2D.fillColor = Color.blue;painter2D.BeginPath();// Move to the arc centerpainter2D.MoveTo(new Vector2(100, 100));// Draw the arc, and close the pathpainter2D.Arc(new Vector2(100, 100), 50.0f, 10.0f, 95.0f);painter2D.ClosePath();// Fill and stroke the pathpainter2D.Fill();painter2D.Stroke();
The following code snippet uses 
ArcTo
to draw an arc of the requested radius in the corner of the lines:

A line with arc

painter2D.BeginPath();painter2D.MoveTo(new Vector2(100, 100));painter2D.ArcTo(new Vector2(150, 150), new Vector2(200, 100), 20.0f);painter2D.LineTo(new Vector2(200, 100));painter2D.Stroke();

Curves

You can use the following methods to draw curves:
  • The 
    BezierCurveTo
     method generates a cubic bezier curve by two control points and the final position of the cubic bezier.
  • The 
    QuadraticCurveTo
     method generates a quadratic bezier curve by a control point and the final position of the quadratic bezier.
The following code snippet uses 
BezierCurveTo
to draw a bezier curve:

A bezier curve

painter2D.BeginPath();painter2D.MoveTo(new Vector2(100, 100));painter2D.BezierCurveTo(new Vector2(150, 150), new Vector2(200, 50), new Vector2(250, 100));painter2D.Stroke();
The following code snippet uses 
QuadraticCurveTo
to draw a quadratic curve:

A quadratic curve

painter2D.BeginPath();painter2D.MoveTo(new Vector2(100, 100));painter2D.QuadraticCurveTo(new Vector2(150, 150), new Vector2(250, 100));painter2D.Stroke();

Holes in fills

You can construct paths with holes in them when you do a 
Fill
. When you call 
MoveTo
, it starts a new sub-path. To create a hole, use the fill rule to overlap the various sub-paths with each other.
The fill rule determines how to fill the inside of a shape:
  • OddEven
    : Draw a ray from that point to infinity in any direction and count the number of path segments from the given shape that the ray crosses. If this number is odd, the point is inside; if even, the point is outside.
  • NonZero
    : Draw a ray from that point to infinity in any direction, and then examine the places where a segment of the shape crosses the ray. Start with a count of zero, and add one each time a path segment crosses the ray from left to right. Subtract one each time a path segment crosses the ray from right to left. After you count the crossings, if the result is zero, then the point is outside the path. Otherwise, it's inside.
The following code snippet creates a rectangle with a diamond shape hole in it:

A rectangle shape with a hole in it

painter2D.BeginPath();painter2D.MoveTo(new Vector2(10, 10));painter2D.LineTo(new Vector2(300, 10));painter2D.LineTo(new Vector2(300, 150));painter2D.LineTo(new Vector2(10, 150));painter2D.ClosePath();painter2D.MoveTo(new Vector2(150, 50));painter2D.LineTo(new Vector2(175, 75));painter2D.LineTo(new Vector2(150, 100));painter2D.LineTo(new Vector2(125, 75));painter2D.ClosePath();painter2D.Fill(FillRule.OddEven);

Additional resources