揭秘 WebGL 光线追踪管线状态：RT 管线配置

            #version 300 es
precision highp float;

uniform vec3 u_cameraPosition;
uniform vec3 u_cameraForward;
uniform vec3 u_cameraUp;
uniform vec3 u_cameraRight;
uniform sampler2D u_sceneTriangles;
uniform sampler2D u_sceneBVH;

// Structure for ray
struct Ray {
    vec3 origin;
    vec3 direction;
};

// Structure for intersection
struct Intersection {
    bool hit;
    float t;
    vec3 position;
    vec3 normal;
};

// Ray/Triangle Intersection (simplified - requires triangle data from the scene)
Intersection intersectTriangle(Ray ray, vec3 v0, vec3 v1, vec3 v2) {
    Intersection intersection;
    intersection.hit = false;
    intersection.t = 1e30;
    // ... (Intersection calculations, simplified)
    return intersection;
}

// Main fragment shader entry point
out vec4 fragColor;

void main() {
    // Calculate screen coordinates to generate the ray.
    vec2 uv = gl_FragCoord.xy / vec2(u_resolution); //u_resolution will contain the screen dimensions
    uv = uv * 2.0 - 1.0;
    vec3 rayDirection = normalize(u_cameraForward + uv.x * u_cameraRight + uv.y * u_cameraUp);
    Ray ray;
    ray.origin = u_cameraPosition;
    ray.direction = rayDirection;

    Intersection closestIntersection;
    closestIntersection.hit = false;
    closestIntersection.t = 1e30;
    
    // Iterate over triangles (simplified - typically uses a BVH)
    for(int i = 0; i < numTriangles; ++i) {
       // Get the triangle data using texture lookups (u_sceneTriangles)
       vec3 v0 = texture(u_sceneTriangles, ...).xyz;
       vec3 v1 = texture(u_sceneTriangles, ...).xyz;
       vec3 v2 = texture(u_sceneTriangles, ...).xyz;
       Intersection intersection = intersectTriangle(ray, v0, v1, v2);
       if (intersection.hit && intersection.t < closestIntersection.t) {
            closestIntersection = intersection;
       }
    }

    // Shading (simplified)
    if (closestIntersection.hit) {
        fragColor = vec4(closestIntersection.normal * 0.5 + 0.5, 1.0);
    } else {
        fragColor = vec4(0.0, 0.0, 0.0, 1.0);
    }
}

            

              
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// Initialization
const canvas = document.getElementById('glCanvas');
const gl = canvas.getContext('webgl2', { antialias: false }); // Or 'webgl' for older browsers
if (!gl) {
    alert('Unable to initialize WebGL. Your browser or hardware may not support it.');
}

// Shader Compilation and Linking (Simplified, requires actual shader source)
function createShader(gl, type, source) {
    const shader = gl.createShader(type);
    gl.shaderSource(shader, source);
    gl.compileShader(shader);
    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        console.error('An error occurred compiling the shaders: ' + gl.getShaderInfoLog(shader));
        gl.deleteShader(shader);
        return null;
    }
    return shader;
}

function createProgram(gl, vertexShader, fragmentShader) {
    const program = gl.createProgram();
    gl.attachShader(program, vertexShader);
    gl.attachShader(program, fragmentShader);
    gl.linkProgram(program);
    if (!gl.getProgramParameter(program, gl.LINK_STATUS)) {
        console.error('Unable to initialize the shader program: ' + gl.getProgramInfoLog(program));
        return null;
    }
    return program;
}

const vertexShaderSource = `
#version 300 es
// ... (Vertex Shader code)
`;
const fragmentShaderSource = `
#version 300 es
precision highp float;
// ... (Fragment Shader code)
`;

const vertexShader = createShader(gl, gl.VERTEX_SHADER, vertexShaderSource);
const fragmentShader = createShader(gl, gl.FRAGMENT_SHADER, fragmentShaderSource);
const shaderProgram = createProgram(gl, vertexShader, fragmentShader);

// Scene Data Preparation (Simplified)
const triangleVertices = new Float32Array([
    0.0, 0.5, 0.0,   // v0
    -0.5, -0.5, 0.0,  // v1
    0.5, -0.5, 0.0   // v2
]);

// Create and bind the vertex buffer (example)
const vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.bufferData(gl.ARRAY_BUFFER, triangleVertices, gl.STATIC_DRAW);

// Get attribute location for vertex positions (example)
const positionAttributeLocation = gl.getAttribLocation(shaderProgram, 'a_position');

// Set attribute pointers (example)
gl.enableVertexAttribArray(positionAttributeLocation);
gl.vertexAttribPointer(positionAttributeLocation, 3, gl.FLOAT, false, 0, 0);

// Set Uniforms (example)
const cameraPositionLocation = gl.getUniformLocation(shaderProgram, 'u_cameraPosition');
gl.useProgram(shaderProgram);
gl.uniform3fv(cameraPositionLocation, [0, 0, 2]); // Example camera position

// Render Loop
function render(now) {
    // Set viewport
    gl.viewport(0, 0, gl.canvas.width, gl.canvas.height);

    // Clear the canvas
    gl.clearColor(0.0, 0.0, 0.0, 1.0); // Clear to black
    gl.clear(gl.COLOR_BUFFER_BIT);

    // Draw the scene (example - requires proper setup of the shader)
    gl.useProgram(shaderProgram);
    gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);  // Rebind if the buffer changes
    gl.vertexAttribPointer(positionAttributeLocation, 3, gl.FLOAT, false, 0, 0);
    gl.drawArrays(gl.TRIANGLES, 0, 3); // Assuming 3 vertices for a triangle

    requestAnimationFrame(render);
}

requestAnimationFrame(render);

            

              
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