标签：游戏开发   shader   unity3d   特效   图形学   

HDR

色调映射 tone-mapping

Middlegrey为全屏幕或部分屏幕的中间灰度，可以控值屏幕的亮度
AvgLogLuminance就是全屏幕或部分屏幕的亮度的对数的平均值
 
AvgLogLuminance的公式
Lw是亮度，n是所取亮度数

这个操作能让L值限制位[0,1)
一些tone-mapping操作用exposure或gamma作为参数控制最终的图像。
tone-mapping是非线性的，他对暗色保有一定范围并且对亮色逐步接近动态
这个技术产生吸引人的视觉效果，有着强烈的对比和细节。

HDR Rendering In OpenGL一文中给出简要且效果不错的公式
 
关键代码如下

			float4 frag(v2f i) :COLOR
			{
				float4 c = tex2D(_MainTex, i.uv_MainTex);
				float y = dot(float4(0.3,0.59,0.11,1),c);
				float yd = _Exp * (_Exp / _BM + 1) / (_Exp + 1);
				return c*yd;
			}

Bloom泛光

权重分布如下，离当前像素越远，权重越低

    double sigma = (double)radius / 3.0;
    double sigma2 = 2.0 * sigma * sigma;
    double sigmap = sigma2 * PI;

    for(long n = 0, i = - radius; i <=radius; ++i)
    {
        long i2 = i * i;
        for(long j = -radius; j <= radius; ++j, ++n)
            kernel[n] = exp(-(double)(i2 + j * j) / sigma2) / sigmap;
     }

针对这个公式我们可以算出3*3，5*5,7*7等滤波器，出于性能考虑，我们还是使用5*5滤波器

 3*3滤波器

			float3 mc00 = tex2D (_MainTex, i.uv_MainTex-fixed2(2,2)/_inten).rgb;
			float3 mc10 = tex2D (_MainTex, i.uv_MainTex-fixed2(1,2)/_inten).rgb;
			float3 mc20 = tex2D (_MainTex, i.uv_MainTex-fixed2(0,2)/_inten).rgb;
			float3 mc30 = tex2D (_MainTex, i.uv_MainTex-fixed2(-1,2)/_inten).rgb;
			float3 mc40 = tex2D (_MainTex, i.uv_MainTex-fixed2(-2,2)/_inten).rgb;

			float3 mc01 = tex2D (_MainTex, i.uv_MainTex-fixed2(2,1)/_inten).rgb;
			float3 mc11 = tex2D (_MainTex, i.uv_MainTex-fixed2(1,1)/_inten).rgb;
			float3 mc21 = tex2D (_MainTex, i.uv_MainTex-fixed2(0,1)/_inten).rgb;
			float3 mc31 = tex2D (_MainTex, i.uv_MainTex-fixed2(-1,1)/_inten).rgb;
			float3 mc41 = tex2D (_MainTex, i.uv_MainTex-fixed2(-2,1)/_inten).rgb;

			float3 mc02 = tex2D (_MainTex, i.uv_MainTex-fixed2(2,0)/_inten).rgb;
			float3 mc12 = tex2D (_MainTex, i.uv_MainTex-fixed2(1,0)/_inten).rgb;
			float3 mc22mc = tex2D (_MainTex, i.uv_MainTex).rgb;
			float3 mc32 = tex2D (_MainTex, i.uv_MainTex-fixed2(-1,0)/_inten).rgb;
			float3 mc42 = tex2D (_MainTex, i.uv_MainTex-fixed2(-2,0)/_inten).rgb;
		
			float3 mc03 = tex2D (_MainTex, i.uv_MainTex-fixed2(2,-1)/_inten).rgb;
			float3 mc13 = tex2D (_MainTex, i.uv_MainTex-fixed2(1,-1)/_inten).rgb;
			float3 mc23 = tex2D (_MainTex, i.uv_MainTex-fixed2(0,-1)/_inten).rgb;
			float3 mc33 = tex2D (_MainTex, i.uv_MainTex-fixed2(-1,-1)/_inten).rgb;
			float3 mc43 = tex2D (_MainTex, i.uv_MainTex-fixed2(-2,-1)/_inten).rgb;

			float3 mc04 = tex2D (_MainTex, i.uv_MainTex-fixed2(2,-2)/_inten).rgb;
			float3 mc14 = tex2D (_MainTex, i.uv_MainTex-fixed2(1,-2)/_inten).rgb;
			float3 mc24 = tex2D (_MainTex, i.uv_MainTex-fixed2(0,-2)/_inten).rgb;
			float3 mc34 = tex2D (_MainTex, i.uv_MainTex-fixed2(-1,-2)/_inten).rgb;
			float3 mc44 = tex2D (_MainTex, i.uv_MainTex-fixed2(-2,-2)/_inten).rgb;
			float3 c=0;
c+=(mc00+mc40+mc04+mc44);//4
c+=4*(mc10+mc30+mc14+mc34+mc01+mc41+mc03+mc43);//16
c+=7*(mc20+mc24+mc02+mc42);//16
c+=16*(mc11+mc13+mc03+mc33);//32
c+=26*(mc21+mc23+mc12+mc32);//64
c+=41*mc22mc;//32
c/=273;

			float lum = Luminance(c);
			c = mc22mc + c * (lum+0.1) * _Lum;
			return float4(c,1);

代码如下：

using UnityEngine;
using System.Collections;
[ExecuteInEditMode]
public class HDRGlow : MonoBehaviour {
    #region Variables
    public Shader curShader;
    private Material curMaterial;
    public float exp = 0.4f;
    public float bm = 0.4f;
    public int inten = 512;
    public float lum = 1f;
    #endregion

    #region Properties
    Material material
    {
        get
        {
            if (curMaterial == null)
            {
                curMaterial = new Material(curShader);
                curMaterial.hideFlags = HideFlags.HideAndDontSave;
            }
            return curMaterial;
        }
    }
    #endregion

    void Start()
    {
        if (!SystemInfo.supportsImageEffects)
        {
            enabled = false;
            return;
        }

        if (!curShader && !curShader.isSupported)
        {
            enabled = false;
        }
    }

    void OnRenderImage(RenderTexture sourceTexture, RenderTexture destTexture)
    {
        if (curShader != null)
        {
            material.SetFloat("_Exp", exp);
            material.SetFloat("_BM", bm);
            material.SetFloat("_Inten", inten);
            material.SetFloat("_Lum", lum);
            Graphics.Blit(sourceTexture, destTexture, material);
        }
        else
        {
            Graphics.Blit(sourceTexture, destTexture);
        }
    }
    void OnDisable()
    {
        if (curMaterial)
        {
            DestroyImmediate(curMaterial);
        }
    }
}

与本文的差别是多了色彩平衡和lens flare效果，可以试着再加上去

                                                        -------  by wolf96 http://blog.csdn.net/wolf96

Unity3d HDR和Bloom效果（高动态范围图像和泛光）

标签：游戏开发   shader   unity3d   特效   图形学   

原文地址：http://blog.csdn.net/wolf96/article/details/44057915