WebGL 着色器统一块：掌握结构化统一数据管理

            uniform PerFrameUniforms {
    mat4 projectionMatrix;
    mat4 viewMatrix;
    vec3 cameraPosition;
    float time;
} perFrame;

            

              
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// Specify the layout qualifier for the uniform block
layout(std140) uniform PerFrameUniforms {
    mat4 projectionMatrix;
    mat4 viewMatrix;
    vec3 cameraPosition;
    float time;
} perFrame;

            

              
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// Assuming you have already created and linked your WebGL program
const program = gl.createProgram();
// ... attach shaders, link program ...

// Get the uniform block index
const blockIndex = gl.getUniformBlockIndex(program, 'PerFrameUniforms');

if (blockIndex === gl.INVALID_INDEX) {
    console.warn('Uniform block PerFrameUniforms not found.');
} else {
    // Query the active uniform block parameters
    const blockSize = gl.getActiveUniformBlockParameter(program, blockIndex, gl.UNIFORM_BLOCK_DATA_SIZE);
    const uniformCount = gl.getActiveUniformBlockParameter(program, blockIndex, gl.UNIFORM_BLOCK_ACTIVE_UNIFORMS);
    const uniformIndices = gl.getActiveUniformBlockParameter(program, blockIndex, gl.UNIFORM_BLOCK_ACTIVE_UNIFORM_INDICES);

    console.log(`Uniform block PerFrameUniforms found:`);
    console.log(`  Size: ${blockSize} bytes`);
    console.log(`  Active Uniforms: ${uniformCount}`);

    // Get names of uniforms within the block
    const uniformNames = [];
    for (let i = 0; i < uniformIndices.length; i++) {
        const uniformInfo = gl.getActiveUniform(program, uniformIndices[i]);
        uniformNames.push(uniformInfo.name);
    }
    console.log(`  Uniforms: ${uniformNames.join(', ')}`);

    // Get the binding point for this uniform block
    // This is crucial for binding the buffer later
    gl.uniformBlockBinding(program, blockIndex, blockIndex); // Using blockIndex as binding point for simplicity
}

            

              
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// Assuming blockIndex is valid

// Get indices of individual uniforms within the block
const uniformIndices = gl.getUniformIndices(program, ['projectionMatrix', 'viewMatrix', 'cameraPosition', 'time']);

// Get offsets and sizes of each uniform
const offsets = gl.getActiveUniforms(program, uniformIndices, gl.UNIFORM_OFFSET);
const sizes = gl.getActiveUniforms(program, uniformIndices, gl.UNIFORM_SIZE);
const types = gl.getActiveUniforms(program, uniformIndices, gl.UNIFORM_TYPE);

// Map uniform names to their offsets and sizes for easier access
const uniformInfoMap = {};
uniformIndices.forEach((index, i) => {
    const uniformName = gl.getActiveUniform(program, index).name;
    uniformInfoMap[uniformName] = {
        offset: offsets[i],
        size: sizes[i], // For arrays, this is the number of elements
        type: types[i]
    };
});

console.log('Uniform offsets and sizes:', uniformInfoMap);

// --- Data Packing ---
// This is the most complex part. You need to pack your data according to std140/std430 rules.
// Let's assume we have our matrices and vectors ready:
const projectionMatrix = new Float32Array([...]); // 16 elements
const viewMatrix = new Float32Array([...]);       // 16 elements
const cameraPosition = new Float32Array([x, y, z, 0.0]); // vec3 is often padded to 4 components
const time = 0.5;

// Create a typed array to hold the packed data. Its size must match blockSize.
const bufferData = new ArrayBuffer(blockSize); // Use blockSize obtained earlier
const dataView = new DataView(bufferData);

// Pack data based on offsets and types (simplified example, actual packing requires careful handling of types and alignment)

// Packing mat4 (std140: 4 vec4 components, each 16 bytes. Total 64 bytes per mat4)
// Each mat4 is effectively 4 vec4s in std140.

// projectionMatrix
const projMatrixInfo = uniformInfoMap['projectionMatrix'];
if (projMatrixInfo) {
    const mat4Bytes = 16 * 4; // 4 rows * 4 components per row, 4 bytes per component
    let offset = projMatrixInfo.offset;
    for (let row = 0; row < 4; row++) {
        for (let col = 0; col < 4; col++) {
            dataView.setFloat32(offset + (row * 4 + col) * 4, projectionMatrix[row * 4 + col], true);
        }
    }
}

// viewMatrix (similar packing)
const viewMatrixInfo = uniformInfoMap['viewMatrix'];
if (viewMatrixInfo) {
    const mat4Bytes = 16 * 4;
    let offset = viewMatrixInfo.offset;
    for (let row = 0; row < 4; row++) {
        for (let col = 0; col < 4; col++) {
            dataView.setFloat32(offset + (row * 4 + col) * 4, viewMatrix[row * 4 + col], true);
        }
    }
}

// cameraPosition (vec3 often packed as vec4 in std140)
const camPosInfo = uniformInfoMap['cameraPosition'];
if (camPosInfo) {
    dataView.setFloat32(camPosInfo.offset, cameraPosition[0], true);
    dataView.setFloat32(camPosInfo.offset + 4, cameraPosition[1], true);
    dataView.setFloat32(camPosInfo.offset + 8, cameraPosition[2], true);
    dataView.setFloat32(camPosInfo.offset + 12, 0.0, true); // Padding
}

// time (float)
const timeInfo = uniformInfoMap['time'];
if (timeInfo) {
    dataView.setFloat32(timeInfo.offset, time, true);
}

// --- Create and Bind Buffer ---
const uniformBuffer = gl.createBuffer();
gl.bindBuffer(gl.UNIFORM_BUFFER, uniformBuffer);
gl.bufferData(gl.UNIFORM_BUFFER, bufferData, gl.DYNAMIC_DRAW); // Or gl.STATIC_DRAW if data doesn't change

// Bind the buffer to the uniform block's binding point
// Use the binding point that was set with gl.uniformBlockBinding earlier
// In our example, we used blockIndex as the binding point.
const bindingPoint = blockIndex;
gl.bindBufferBase(gl.UNIFORM_BUFFER, bindingPoint, uniformBuffer);

            

              
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// Assuming uniformBuffer, bufferData, dataView, and uniformInfoMap are accessible

// Update your data variables...
const newTime = performance.now() / 1000.0;
const updatedCameraPosition = [...currentCamera.position.toArray(), 0.0];

// Re-pack only changed data for efficiency
const timeInfo = uniformInfoMap['time'];
if (timeInfo) {
    dataView.setFloat32(timeInfo.offset, newTime, true);
}

const camPosInfo = uniformInfoMap['cameraPosition'];
if (camPosInfo) {
    dataView.setFloat32(camPosInfo.offset, updatedCameraPosition[0], true);
    dataView.setFloat32(camPosInfo.offset + 4, updatedCameraPosition[1], true);
    dataView.setFloat32(camPosInfo.offset + 8, updatedCameraPosition[2], true);
    dataView.setFloat32(camPosInfo.offset + 12, 0.0, true); // Padding
}

// Update the buffer on the GPU
gl.bindBuffer(gl.UNIFORM_BUFFER, uniformBuffer);
gl.bufferSubData(gl.UNIFORM_BUFFER, 0, bufferData); // Update the entire buffer, or specify offsets

            

              
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// During program setup or when switching programs:
const blockIndex = gl.getUniformBlockIndex(program, 'PerFrameUniforms');
const bindingPoint = blockIndex; // Or any other desired binding point index (0-15 typically)

if (blockIndex !== gl.INVALID_INDEX) {
    gl.uniformBlockBinding(program, blockIndex, bindingPoint);
    // Later, when binding buffers:
    // gl.bindBufferBase(gl.UNIFORM_BUFFER, bindingPoint, yourUniformBuffer);
}

            

              
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