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笔刷大小调节

上面的代码中其实我们已经提供了笔刷大小的字段，即brushSize，现在只需要将该字段和界面中的Slider绑定即可，Slider值的范围我们设置为1~20

代码中只需要做如下改动：

public Slider brushSizeSlider; //控制笔刷大小的滑动条
public float brushSize => brushSizeSlider.value;    //笔刷大小取滑动条的值

完整代码如下：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;public class Painter : MonoBehaviour
{public RenderTexture renderTexture;public Slider brushSizeSlider;public Texture2D brushTexture; //笔刷纹理public float brushSize => brushSizeSlider.value;    //笔刷大小public float resolutionMultiplier = 5;  //线性插值密度调节private Vector2 previousMousePos; //记录上一帧鼠标的位置  void Update(){if (Input.GetMouseButtonDown(0)){previousMousePos = Input.mousePosition;}if (Input.GetMouseButton(0)){var mousePosition = Input.mousePosition;DrawLine(previousMousePos, mousePosition);previousMousePos = mousePosition;}}private void DrawLine(Vector2 start, Vector2 end){float distance = Vector2.Distance(start, end);int steps = Mathf.CeilToInt(distance * resolutionMultiplier);for (int i = 0; i <= steps; i++){float t = i / (float)steps;int x = Mathf.FloorToInt(Mathf.Lerp(start.x, end.x, t));int y = Mathf.FloorToInt(Mathf.Lerp(start.y, end.y, t));DrawBrush(x, y);}}private void DrawBrush(int x, int y){Rect brushRect = new Rect(x, y, brushSize, brushSize);Graphics.SetRenderTarget(renderTexture);GL.PushMatrix();GL.LoadPixelMatrix(0, renderTexture.width, 0, renderTexture.height);Graphics.DrawTexture(brushRect, brushTexture);GL.PopMatrix();Graphics.SetRenderTarget(null);}}

效果优化 

运行效果如下图，可见虽然笔刷粗细已可以调节，但是在调节过程中，滑动的同时滑动条周围有绘制的线条，这本不该出现的，出现的原因是因为我们监听了鼠标按下的事件来绘制，这导致在操作滑动条的时候，绘制依然在进行。

操作UI时屏蔽绘制

我们需要检测当前的鼠标是否在UI元素上，如果在，则不进行绘制，这可以使用EventSystem的射线检测来实现，如下我们定义一个函数，当光标在UI元素上的时候返回true，否则返回false：

private bool IsPointerOverUIElement()
{PointerEventData eventData = new PointerEventData(EventSystem.current);eventData.position = Input.mousePosition;List<RaycastResult> results = new List<RaycastResult>();EventSystem.current.RaycastAll(eventData, results);return results.Count > 0;
}

我们在鼠标左键点击的时候判断是否在UI元素上，如果在则禁止绘制；

但有个问题，我们用来绘制的RawImage也是UI元素，它铺满整个屏幕，这会导致我们始终没办法绘制，我们可以将其Raycast Target关掉，这样再操作UI元素的时候就不会进行多余的绘制了

完整代码如下：

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using UnityEngine.UI;public class Painter : MonoBehaviour
{public RenderTexture renderTexture;public Slider brushSizeSlider; //控制笔刷大小的滑动条public Texture2D brushTexture; //笔刷纹理public float brushSize => brushSizeSlider.value;    //笔刷大小取滑动条的值public float resolutionMultiplier = 5;  //线性插值密度调节private Vector2 previousMousePos; //记录上一帧鼠标的位置  private bool startFromUIElement = false; //点击是否是从UI元素上开始的void Update(){//判断光标是否在UI元素上if (Input.GetMouseButtonDown(0)){if (IsPointerOverUIElement()){startFromUIElement = true;}previousMousePos = Input.mousePosition;}if (Input.GetMouseButton(0) && !startFromUIElement){var mousePosition = Input.mousePosition;DrawLine(previousMousePos, mousePosition);previousMousePos = mousePosition;}if (Input.GetMouseButtonUp(0)){startFromUIElement = false;}}private void DrawLine(Vector2 start, Vector2 end){float distance = Vector2.Distance(start, end);int steps = Mathf.CeilToInt(distance * resolutionMultiplier);for (int i = 0; i <= steps; i++){float t = i / (float)steps;int x = Mathf.FloorToInt(Mathf.Lerp(start.x, end.x, t));int y = Mathf.FloorToInt(Mathf.Lerp(start.y, end.y, t));DrawBrush(x, y);}}private void DrawBrush(int x, int y){Rect brushRect = new Rect(x, y, brushSize, brushSize);Graphics.SetRenderTarget(renderTexture);GL.PushMatrix();GL.LoadPixelMatrix(0, renderTexture.width, 0, renderTexture.height);Graphics.DrawTexture(brushRect, brushTexture);GL.PopMatrix();Graphics.SetRenderTarget(null);}private bool IsPointerOverUIElement(){PointerEventData eventData = new PointerEventData(EventSystem.current);eventData.position = Input.mousePosition;List<RaycastResult> results = new List<RaycastResult>();EventSystem.current.RaycastAll(eventData, results);return results.Count > 0;}}

在下一节我将为大家介绍如何调节线条的颜色~