[question 008: what is UV in unity?]

Video Explanation

Unity Chinese vs UV The understanding of the

One 、 What is? UV

UV What is it? ？UV In fact, it is another definition of texture coordinate axis ;
For example, we usually say Transform Coordinates of , That is to say Transform Specific position in Cartesian coordinate system , The visual representation of the location is (x,y,z); So usually when we talk about the coordinates of objects , The subconscious mind will think (x,y,z);

Why do textures have coordinates ？
For example, this picture below ：

From this picture we can view its information , Know this picture size How much is the , What's the size , When was it created , But we don't care about the coordinates of this picture , Because we don't use its coordinates at this time , But it does exist .

When we put the above texture on a Quad When it's up there , You need to use the coordinates of the texture ： Look at the following effect ：

Above is the picture Unity The effect of operation , Among them is 5 The two are equal in size Quad, But they use the same texture to get different results ; This is because every Quad Of the texture obtained UV The coordinate ranges are different , Lead to Quad The rendering results are different ;

Two 、 The example analysis

UV The meaning of coordinates lies in a mapping relationship with object coordinates ;
For example, the texture size in the above figure is 512x512, We can't use 512*512 This size to map , If we are mapping to objects of the same size , They are 1 Yes 1 The relationship between , That is, the coordinates and texture of each object UV The coordinate points correspond to ; Otherwise, the mapping process is very troublesome ;

So what are object coordinates ？
Look at one below Quad Pictures of the ：

The object in the above figure Pivot and Center All in the center , In wireframe mode, you can see that the object has 4 vertices ,2 Triangles ; To put all or part of a texture completely in this quad It shows correctly , It needs to be used uv coordinate , The following steps are required ：

• To find the Quad Rendering of triangles , Is it counterclockwise or clockwise ; You will get a picture of the front or the back
• To find the Quad Of 4 individual UV The order of coordinates , That is to confirm uv[0]、uv[1]、uv[2]、uv[3] And vertex coordinates vertext[0]、vertext[1]、vertext[2]、vertext[3] Correspondence of , Only the correct correspondence can get the correct result ; You can use it here UV Any reasonable range of coordinates 4 individual uv Coordinate points to correspond to vertex coordinates , In this way, some or all of the texture can be rendered to quad On ;
• uv The value range of coordinates will be converted to 0-1 Between ; such as 512 The size picture range will be changed to ：uv(0/512,0/512)-(512/512,512/512) Value range of , Convert according to image size ;
• Finally, reset the object UV Coordinates are OK ;

UV Is another name for texture coordinates ,UV The coordinates are xy coordinate , It is only for the convenience of describing the differences in the process that this statement is made ; So deal with uv Coordinates deal with Cartesian coordinates ; You can think of a texture as the first quadrant in a Cartesian coordinate system , In the lower left corner （0,0） coordinate , The maximum value range of the first quadrant of this coordinate is 0-1 Between ;

The mapping between texture and object is the mapping relationship between texture coordinates and object coordinates , The correct mapping of texture coordinates can get the correct appearance of the object .

3、 ... and 、 Source code

using System.Collections;
using System.Collections.Generic;
using System.Linq;
using UnityEngine;

public class ValakiShowUvPartDemos : MonoBehaviour
{
    
    enum ShowUVPartType
    {
    
        None=0,
        LeftTop,
        LeftBottom,
        Center,
        RightTop,
        RightBottom
    };

    List<Vector2> uvs;
    Vector2[] backUv;
    Mesh mesh; 
    [SerializeField] ShowUVPartType showUVPartType;

    [SerializeField] bool isPlayRandomUvPart;

    ShowUVPartType currentUvPartType = ShowUVPartType.None;
    private void Awake()
    {
    
        mesh = GetComponent<MeshFilter>().mesh;
        uvs = mesh.uv.ToList();
        backUv = mesh.uv;
    }

    float totalTime;
    private void LateUpdate()
    {
    
        if (isPlayRandomUvPart)
        {
    

            totalTime += Time.deltaTime;
            if(totalTime >= 0.7f)
            {
    
                totalTime = 0;
                int random = Random.Range(1, 6);
                showUVPartType = (ShowUVPartType)random;
            }
          
        }

        if (currentUvPartType != showUVPartType)
        {
    
            currentUvPartType = showUVPartType;
            switch (showUVPartType)
            {
    
                case ShowUVPartType.Center:
                    mesh.SetUVs(0, backUv);
                    break;
                case ShowUVPartType.LeftBottom:
                    ShowLeftBottomUvPart();
                    break;
                case ShowUVPartType.LeftTop:
                    ShowLeftTopUvPart();
                    break;
                case ShowUVPartType.RightBottom:
                    ShowRightBottomUvPart();
                    break;
                case ShowUVPartType.RightTop:
                    ShowRightTopUvPart();
                    break;
            }
        }
    }

   


    void ShowLeftTopUvPart()
    {
    
        // Left - The lower right - Top left - The upper right 
        uvs[0] = new Vector2(0, 0.75f);
        uvs[1] = new Vector2(0.25f, 0.75f); 
        uvs[2] = new Vector2(0, 1);
        uvs[3] = new Vector2(0.25f, 1); 
       
        mesh.SetUVs(0, uvs);
    }


    void ShowRightTopUvPart()
    {
    
        
        uvs[0] = new Vector2(0.75f, 0.75f);
        uvs[1] = new Vector2(1, 0.75f);
        uvs[2] = new Vector2(0.75f, 1);
        uvs[3] = new Vector2(1, 1);

        mesh.SetUVs(0, uvs);
    }


    void ShowLeftBottomUvPart()
    {
    
        
        uvs[0] = new Vector2(0, 0);
        uvs[1] = new Vector2(0.25f, 0);
        uvs[2] = new Vector2(0, 0.25f);
        uvs[3] = new Vector2(0.25f, 0.25f);

        mesh.SetUVs(0, uvs);
    }


    void ShowRightBottomUvPart()
    {
    

        uvs[0] = new Vector2(0.75f, 0);
        uvs[1] = new Vector2(1, 0);
        uvs[2] = new Vector2(0.75f, 0.25f);
        uvs[3] = new Vector2(1, 0.25f);

        mesh.SetUVs(0, uvs);
    }


}

Conclusion ：

Don't ask me how many grades , I'm just a jerk 【valaki】