为什么这个灯光代码仅适用于单灯并在我添加多个灯时断开？

Question

我正在尝试使用lwjgl和java创建一个简单的2D游戏引擎。但是我在灯光编程过程中遇到了困难，因为我编写的代码仅在场景中有一个灯光而不是在我添加多个灯光时才有效。我只是想不通为什么所以我决定在这里问。

这是带有光照计算的片段着色器：

#version 330 core

layout (location = 0) out vec4 color;
layout (origin_upper_left, pixel_center_integer) in vec4 gl_FragCoord;

in DATA {
    vec2 tc;
} fs_in;

uniform sampler2D tex;

float map(float value, float min1, float max1, float min2, float max2) {
  return min2 + (value - min1) * (max2 - min2) / (max1 - min1);
}

void main() {
    vec3 lightColor = vec3(1, 1, 1);
    float range = 700;
    float x = 200;
    float y = 200;
    float ambient = 0.1;
    float intensity = 0.8;
    float alpha = 1.0;

    vec3 totalDiffuse = vec3(0.0);

    for(int i=0;i<1;i++){
        alpha = 1-map(distance(gl_FragCoord.xy, vec2(x*i, y*i)), 0.0, range, 0.0, 1.0);
        totalDiffuse += alpha*lightColor;
    }

    totalDiffuse = max(totalDiffuse, ambient);

    color = vec4(totalDiffuse, 1.0) * texture(tex, fs_in.tc);
}

如果我在场景中只使用一个灯光运行此代码，即设置for循环运行的时间为1，那么它可以正常工作并创建如下所示：

但是当我将它改为循环例如3次时，你会期望它创建3个不同的灯，但实际上它只是增加了第一个灯的光强度，如下所示：

谁知道为什么？

Answer 1

这个词的结果

alpha = 1-map(distance(gl_FragCoord.xy, vec2(x*i, y*i)), 0.0, range, 0.0, 1.0);

可能是消极的。

这将导致totalDiffuse减少。

把alpha夹到最低0：

//totalDiffuse += alpha*lightColor;
totalDiffuse += max(0.0, alpha) * lightColor;

注意，光源之间的距离是length(vec2(200, 200))，但每个光源的照射范围（半径）是700.所以无论如何光源都是重叠的。

---

我建议使用glsl函数smoothstep，它在两个值之间执行Hermite interpolation。

请尝试以下方法：

for(int i=0; i<3; i++ )
{
    vec2 pos = vec2(x, y) * float(i);
    float dist = distance(gl_FragCoord.xy, pos);

    alpha = smoothstep(50.0, 100.0, dist);
    totalDiffuse += clamp(1.0-alpha, 0.0, 1.0) * lightColor;
}

在这种情况下，smoothstep的第二个参数（100.0）是光源的最大半径，第一个参数（50.0）是全光的半径。

---

请参阅我使用smoothstep的WebGL示例：

(function loadscene() {    

var canvas, gl, vp_size, prog, bufObj = {};

function initScene() {

    canvas = document.getElementById( "ogl-canvas");
    gl = canvas.getContext( "experimental-webgl" );
    if ( !gl )
      return;

    progDraw = gl.createProgram();
    for (let i = 0; i < 2; ++i) {
        let source = document.getElementById(i==0 ? "draw-shader-vs" : "draw-shader-fs").text;
        let shaderObj = gl.createShader(i==0 ? gl.VERTEX_SHADER : gl.FRAGMENT_SHADER);
        gl.shaderSource(shaderObj, source);
        gl.compileShader(shaderObj);
        let status = gl.getShaderParameter(shaderObj, gl.COMPILE_STATUS);
        if (!status) alert(gl.getShaderInfoLog(shaderObj));
        gl.attachShader(progDraw, shaderObj);
        gl.linkProgram(progDraw);
    }
    status = gl.getProgramParameter(progDraw, gl.LINK_STATUS);
    if ( !status ) alert(gl.getProgramInfoLog(progDraw));
    progDraw.inPos = gl.getAttribLocation(progDraw, "inPos");
    progDraw.u_time = gl.getUniformLocation(progDraw, "u_time");
    progDraw.u_resolution = gl.getUniformLocation(progDraw, "u_resolution");
    gl.useProgram(progDraw);

    var pos = [ -1, -1, 1, -1, 1, 1, -1, 1 ];
    var inx = [ 0, 1, 2, 0, 2, 3 ];
    bufObj.pos = gl.createBuffer();
    gl.bindBuffer( gl.ARRAY_BUFFER, bufObj.pos );
    gl.bufferData( gl.ARRAY_BUFFER, new Float32Array( pos ), gl.STATIC_DRAW );
    bufObj.inx = gl.createBuffer();
    bufObj.inx.len = inx.length;
    gl.bindBuffer( gl.ELEMENT_ARRAY_BUFFER, bufObj.inx );
    gl.bufferData( gl.ELEMENT_ARRAY_BUFFER, new Uint16Array( inx ), gl.STATIC_DRAW );
    gl.enableVertexAttribArray( progDraw.inPos );
    gl.vertexAttribPointer( progDraw.inPos, 2, gl.FLOAT, false, 0, 0 ); 
    
    gl.enable( gl.DEPTH_TEST );
    gl.clearColor( 0.0, 0.0, 0.0, 1.0 );

    window.onresize = resize;
    resize();
    requestAnimationFrame(render);
}

function resize() {
    //vp_size = [gl.drawingBufferWidth, gl.drawingBufferHeight];
    vp_size = [window.innerWidth, window.innerHeight];
    //vp_size = [256, 256]
    canvas.width = vp_size[0];
    canvas.height = vp_size[1];
}

function render(deltaMS) {

    gl.viewport( 0, 0, canvas.width, canvas.height );
    gl.clear( gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT );
   
    gl.uniform1f(progDraw.u_time, deltaMS/2000.0);
    gl.uniform2f(progDraw.u_resolution, canvas.width, canvas.height);
    gl.drawElements( gl.TRIANGLES, bufObj.inx.len, gl.UNSIGNED_SHORT, 0 );
    
    requestAnimationFrame(render);
}  

initScene();

})();

<script id="draw-shader-vs" type="x-shader/x-vertex">
precision mediump float;
attribute vec2 inPos;

void main() {
    gl_Position = vec4( inPos.xy, 0.0, 1.0 );
}
</script>

<script id="draw-shader-fs" type="x-shader/x-fragment">
precision mediump float;
uniform float u_time;
uniform vec2 u_resolution;

vec3 HUEtoRGB(in float H)
{
    float R = abs(H * 6.0 - 3.0) - 1.0;
    float G = 2.0 - abs(H * 6.0 - 2.0);
    float B = 2.0 - abs(H * 6.0 - 4.0);
    return clamp( vec3(R,G,B), 0.0, 1.0 );
}

void main() {
    vec2 uv = gl_FragCoord.xy / u_resolution;

    vec3 lightColor = vec3(1, 1, 1);
    float range = length(u_resolution) / 4.0;
    float x = u_resolution.x / 4.0;
    float y = u_resolution.y / 4.0;
    float ambient = 0.1;
    float intensity = 0.8;
    float alpha = 1.0;

    vec3 totalDiffuse = vec3(0.0);

    for(int i=0;i<3;i++)
    {    
        vec2 pos = vec2(x, y) * float(i+1);
        float dist = distance(gl_FragCoord.xy, pos);
        
        alpha = smoothstep(range/4.0, range/2.0, dist);
        totalDiffuse += clamp(1.0-alpha, 0.0, 1.0) * lightColor;
    }
    totalDiffuse = max(totalDiffuse, ambient);

    vec4 texcol = vec4( 1.0-uv.x, 1.0-uv.y, uv.x*uv.y, 1.0 );
    gl_FragColor = vec4(totalDiffuse, 1.0) * texcol;
}
</script>

<canvas id="ogl-canvas" style="border: none"></canvas>