MinaGabriel · November 25, 2020 14:28
diff --git a/Shadow.html b/Shadow.html
 <!DOCTYPE html>
 <html lang="en">
 <head>
    <meta charset="utf-8"/>
    <title>Translate a Triangle</title>

 <body onload="main()">
 <canvas id="webgl" width="400" height="400">
    Please use a browser that supports "canvas"
 </canvas>
 </body>

 <script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-utils.js"></script>
 <script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-debug.js"></script>
 <script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-utils.js"></script>
 <script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-matrix.js"></script>
 <script type="text/javascript">
    // Shadow.js (c) 2012 matsuda and tanaka
    // Vertex shader program for generating a shadow map
    var SHADOW_VSHADER_SOURCE =
        'attribute vec4 a_Position;\n' +
        'uniform mat4 u_MvpMatrix;\n' +
        'void main() {\n' +
        '  gl_Position = u_MvpMatrix * a_Position;\n' +
        '}\n';

    // Fragment shader program for generating a shadow map
    var SHADOW_FSHADER_SOURCE =
        '#ifdef GL_ES\n' +
        'precision mediump float;\n' +
        '#endif\n' +
        'void main() {\n' +
        '  gl_FragColor = vec4(gl_FragCoord.z, 0.0, 0.0, 0.0);\n' + // Write the z-value in R
        '}\n';

    // Vertex shader program for regular drawing
    var VSHADER_SOURCE =
        'attribute vec4 a_Position;\n' +
        'attribute vec4 a_Color;\n' +
        'uniform mat4 u_MvpMatrix;\n' +
        'uniform mat4 u_MvpMatrixFromLight;\n' +
        'varying vec4 v_PositionFromLight;\n' +
        'varying vec4 v_Color;\n' +
        'void main() {\n' +
        '  gl_Position = u_MvpMatrix * a_Position;\n' +
        '  v_PositionFromLight = u_MvpMatrixFromLight * a_Position;\n' +
        '  v_Color = a_Color;\n' +
        '}\n';

    // Fragment shader program for regular drawing
    var FSHADER_SOURCE =
        '#ifdef GL_ES\n' +
        'precision mediump float;\n' +
        '#endif\n' +
        'uniform sampler2D u_ShadowMap;\n' +
        'varying vec4 v_PositionFromLight;\n' +
        'varying vec4 v_Color;\n' +
        'void main() {\n' +
        '  vec3 shadowCoord = (v_PositionFromLight.xyz/v_PositionFromLight.w)/2.0 + 0.5;\n' +
        '  vec4 rgbaDepth = texture2D(u_ShadowMap, shadowCoord.xy);\n' +
        '  float depth = rgbaDepth.r;\n' + // Retrieve the z-value from R
        '  float visibility = (shadowCoord.z > depth + 0.005) ? 0.7 : 1.0;\n' +
        '  gl_FragColor = vec4(v_Color.rgb * visibility, v_Color.a);\n' +
        '}\n';

    var OFFSCREEN_WIDTH = 2048, OFFSCREEN_HEIGHT = 2048;
    var LIGHT_X = 0, LIGHT_Y = 7, LIGHT_Z = 2; // Position of the light source

    function main() {
        // Retrieve <canvas> element
        var canvas = document.getElementById('webgl');

        // Get the rendering context for WebGL
        var gl = getWebGLContext(canvas);
        if (!gl) {
            console.log('Failed to get the rendering context for WebGL');
            return;
        }

        // Initialize shaders for generating a shadow map
        var shadowProgram = createProgram(gl, SHADOW_VSHADER_SOURCE, SHADOW_FSHADER_SOURCE);
        shadowProgram.a_Position = gl.getAttribLocation(shadowProgram, 'a_Position');
        shadowProgram.u_MvpMatrix = gl.getUniformLocation(shadowProgram, 'u_MvpMatrix');
        if (shadowProgram.a_Position < 0 || !shadowProgram.u_MvpMatrix) {
            console.log('Failed to get the storage location of attribute or uniform variable from shadowProgram');
            return;
        }

        // Initialize shaders for regular drawing
        var normalProgram = createProgram(gl, VSHADER_SOURCE, FSHADER_SOURCE);
        normalProgram.a_Position = gl.getAttribLocation(normalProgram, 'a_Position');
        normalProgram.a_Color = gl.getAttribLocation(normalProgram, 'a_Color');
        normalProgram.u_MvpMatrix = gl.getUniformLocation(normalProgram, 'u_MvpMatrix');
        normalProgram.u_MvpMatrixFromLight = gl.getUniformLocation(normalProgram, 'u_MvpMatrixFromLight');
        normalProgram.u_ShadowMap = gl.getUniformLocation(normalProgram, 'u_ShadowMap');
        if (normalProgram.a_Position < 0 || normalProgram.a_Color < 0 || !normalProgram.u_MvpMatrix ||
            !normalProgram.u_MvpMatrixFromLight || !normalProgram.u_ShadowMap) {
            console.log('Failed to get the storage location of attribute or uniform variable from normalProgram');
            return;
        }

        // Set the vertex information
        var triangle = initVertexBuffersForTriangle(gl);
        var plane = initVertexBuffersForPlane(gl);
        if (!triangle || !plane) {
            console.log('Failed to set the vertex information');
            return;
        }

        // Initialize framebuffer object (FBO)
        var fbo = initFramebufferObject(gl);
        if (!fbo) {
            console.log('Failed to initialize frame buffer object');
            return;
        }
        gl.activeTexture(gl.TEXTURE0); // Set a texture object to the texture unit
        gl.bindTexture(gl.TEXTURE_2D, fbo.texture);

        // Set the clear color and enable the depth test
        gl.clearColor(0, 0, 0, 1);
        gl.enable(gl.DEPTH_TEST);

        var viewProjMatrixFromLight = new Matrix4(); // Prepare a view projection matrix for generating a shadow map
        viewProjMatrixFromLight.setPerspective(70.0, OFFSCREEN_WIDTH/OFFSCREEN_HEIGHT, 1.0, 100.0);
        viewProjMatrixFromLight.lookAt(LIGHT_X, LIGHT_Y, LIGHT_Z, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

        var viewProjMatrix = new Matrix4();          // Prepare a view projection matrix for regular drawing
        viewProjMatrix.setPerspective(45, canvas.width/canvas.height, 1.0, 100.0);
        viewProjMatrix.lookAt(0.0, 7.0, 9.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

        var currentAngle = 0.0; // Current rotation angle (degrees)
        var mvpMatrixFromLight_t = new Matrix4(); // A model view projection matrix from light source (for triangle)
        var mvpMatrixFromLight_p = new Matrix4(); // A model view projection matrix from light source (for plane)
        var tick = function() {
            currentAngle = animate(currentAngle);

            gl.bindFramebuffer(gl.FRAMEBUFFER, fbo);               // Change the drawing destination to FBO
            gl.viewport(0, 0, OFFSCREEN_HEIGHT, OFFSCREEN_HEIGHT); // Set view port for FBO
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);   // Clear FBO

            gl.useProgram(shadowProgram); // Set shaders for generating a shadow map
            // Draw the triangle and the plane (for generating a shadow map)
            drawTriangle(gl, shadowProgram, triangle, currentAngle, viewProjMatrixFromLight);
            mvpMatrixFromLight_t.set(g_mvpMatrix); // Used later
            drawPlane(gl, shadowProgram, plane, viewProjMatrixFromLight);
            mvpMatrixFromLight_p.set(g_mvpMatrix); // Used later

            gl.bindFramebuffer(gl.FRAMEBUFFER, null);               // Change the drawing destination to color buffer
            gl.viewport(0, 0, canvas.width, canvas.height);
            gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);    // Clear color and depth buffer

            gl.useProgram(normalProgram); // Set the shader for regular drawing
            gl.uniform1i(normalProgram.u_ShadowMap, 0);  // Pass 0 because gl.TEXTURE0 is enabledする
            // Draw the triangle and plane ( for regular drawing)
            gl.uniformMatrix4fv(normalProgram.u_MvpMatrixFromLight, false, mvpMatrixFromLight_t.elements);
            drawTriangle(gl, normalProgram, triangle, currentAngle, viewProjMatrix);
            gl.uniformMatrix4fv(normalProgram.u_MvpMatrixFromLight, false, mvpMatrixFromLight_p.elements);
            drawPlane(gl, normalProgram, plane, viewProjMatrix);

            window.requestAnimationFrame(tick, canvas);
        };
        tick();
    }

    // Coordinate transformation matrix
    var g_modelMatrix = new Matrix4();
    var g_mvpMatrix = new Matrix4();
    function drawTriangle(gl, program, triangle, angle, viewProjMatrix) {
        // Set rotate angle to model matrix and draw triangle
        g_modelMatrix.setRotate(angle, 0, 1, 0);
        draw(gl, program, triangle, viewProjMatrix);
    }

    function drawPlane(gl, program, plane, viewProjMatrix) {
        // Set rotate angle to model matrix and draw plane
        g_modelMatrix.setRotate(-45, 0, 1, 1);
        draw(gl, program, plane, viewProjMatrix);
    }

    function draw(gl, program, o, viewProjMatrix) {
        initAttributeVariable(gl, program.a_Position, o.vertexBuffer);
        if (program.a_Color != undefined) // If a_Color is defined to attribute
            initAttributeVariable(gl, program.a_Color, o.colorBuffer);

        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, o.indexBuffer);

        // Calculate the model view project matrix and pass it to u_MvpMatrix
        g_mvpMatrix.set(viewProjMatrix);
        g_mvpMatrix.multiply(g_modelMatrix);
        gl.uniformMatrix4fv(program.u_MvpMatrix, false, g_mvpMatrix.elements);

        gl.drawElements(gl.TRIANGLES, o.numIndices, gl.UNSIGNED_BYTE, 0);
    }

    // Assign the buffer objects and enable the assignment
    function initAttributeVariable(gl, a_attribute, buffer) {
        gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
        gl.vertexAttribPointer(a_attribute, buffer.num, buffer.type, false, 0, 0);
        gl.enableVertexAttribArray(a_attribute);
    }

    function initVertexBuffersForPlane(gl) {
        // Create a plane
        //  v1------v0
        //  |        |
        //  |        |
        //  |        |
        //  v2------v3

        // Vertex coordinates
        var vertices = new Float32Array([
            3.0, -1.7, 2.5,  -3.0, -1.7, 2.5,  -3.0, -1.7, -2.5,   3.0, -1.7, -2.5    // v0-v1-v2-v3
        ]);

        // Colors
        var colors = new Float32Array([
            1.0, 1.0, 1.0,    1.0, 1.0, 1.0,  1.0, 1.0, 1.0,   1.0, 1.0, 1.0
        ]);

        // Indices of the vertices
        var indices = new Uint8Array([0, 1, 2,   0, 2, 3]);

        var o = new Object(); // Utilize Object object to return multiple buffer objects together

        // Write vertex information to buffer object
        o.vertexBuffer = initArrayBufferForLaterUse(gl, vertices, 3, gl.FLOAT);
        o.colorBuffer = initArrayBufferForLaterUse(gl, colors, 3, gl.FLOAT);
        o.indexBuffer = initElementArrayBufferForLaterUse(gl, indices, gl.UNSIGNED_BYTE);
        if (!o.vertexBuffer || !o.colorBuffer || !o.indexBuffer) return null;

        o.numIndices = indices.length;

        // Unbind the buffer object
        gl.bindBuffer(gl.ARRAY_BUFFER, null);
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

        return o;
    }

    function initVertexBuffersForTriangle(gl) {
        // Create a triangle
        //       v2
        //      / |
        //     /  |
        //    /   |
        //  v0----v1

        // Vertex coordinates
        var vertices = new Float32Array([-0.8, 3.5, 0.0,  0.8, 3.5, 0.0,  0.0, 3.5, 1.8]);
        // Colors
        var colors = new Float32Array([1.0, 0.5, 0.0,  1.0, 0.5, 0.0,  1.0, 0.0, 0.0]);
        // Indices of the vertices
        var indices = new Uint8Array([0, 1, 2]);

        var o = new Object();  // Utilize Object object to return multiple buffer objects together

        // Write vertex information to buffer object
        o.vertexBuffer = initArrayBufferForLaterUse(gl, vertices, 3, gl.FLOAT);
        o.colorBuffer = initArrayBufferForLaterUse(gl, colors, 3, gl.FLOAT);
        o.indexBuffer = initElementArrayBufferForLaterUse(gl, indices, gl.UNSIGNED_BYTE);
        if (!o.vertexBuffer || !o.colorBuffer || !o.indexBuffer) return null;

        o.numIndices = indices.length;

        // Unbind the buffer object
        gl.bindBuffer(gl.ARRAY_BUFFER, null);
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

        return o;
    }

    function initArrayBufferForLaterUse(gl, data, num, type) {
        // Create a buffer object
        var buffer = gl.createBuffer();
        if (!buffer) {
            console.log('Failed to create the buffer object');
            return null;
        }
        // Write date into the buffer object
        gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
        gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);

        // Store the necessary information to assign the object to the attribute variable later
        buffer.num = num;
        buffer.type = type;

        return buffer;
    }

    function initElementArrayBufferForLaterUse(gl, data, type) {
        // Create a buffer object
        var buffer = gl.createBuffer();
        if (!buffer) {
            console.log('Failed to create the buffer object');
            return null;
        }
        // Write date into the buffer object
        gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, buffer);
        gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, data, gl.STATIC_DRAW);

        buffer.type = type;

        return buffer;
    }

    function initFramebufferObject(gl) {
        var framebuffer, texture, depthBuffer;

        // Define the error handling function
        var error = function() {
            if (framebuffer) gl.deleteFramebuffer(framebuffer);
            if (texture) gl.deleteTexture(texture);
            if (depthBuffer) gl.deleteRenderbuffer(depthBuffer);
            return null;
        }

        // Create a framebuffer object (FBO)
        framebuffer = gl.createFramebuffer();
        if (!framebuffer) {
            console.log('Failed to create frame buffer object');
            return error();
        }

        // Create a texture object and set its size and parameters
        texture = gl.createTexture(); // Create a texture object
        if (!texture) {
            console.log('Failed to create texture object');
            return error();
        }
        gl.bindTexture(gl.TEXTURE_2D, texture);
        gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, OFFSCREEN_WIDTH, OFFSCREEN_HEIGHT, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
        gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);

        // Create a renderbuffer object and Set its size and parameters
        depthBuffer = gl.createRenderbuffer(); // Create a renderbuffer object
        if (!depthBuffer) {
            console.log('Failed to create renderbuffer object');
            return error();
        }
        gl.bindRenderbuffer(gl.RENDERBUFFER, depthBuffer);
        gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, OFFSCREEN_WIDTH, OFFSCREEN_HEIGHT);

        // Attach the texture and the renderbuffer object to the FBO
        gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
        gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
        gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, depthBuffer);

        // Check if FBO is configured correctly
        var e = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
        if (gl.FRAMEBUFFER_COMPLETE !== e) {
            console.log('Frame buffer object is incomplete: ' + e.toString());
            return error();
        }

        framebuffer.texture = texture; // keep the required object

        // Unbind the buffer object
        gl.bindFramebuffer(gl.FRAMEBUFFER, null);
        gl.bindTexture(gl.TEXTURE_2D, null);
        gl.bindRenderbuffer(gl.RENDERBUFFER, null);

        return framebuffer;
    }

    var ANGLE_STEP = 40;   // The increments of rotation angle (degrees)

    var last = Date.now(); // Last time that this function was called
    function animate(angle) {
        var now = Date.now();   // Calculate the elapsed time
        var elapsed = now - last;
        last = now;
        // Update the current rotation angle (adjusted by the elapsed time)
        var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;
        return newAngle % 360;
    }


 </script>
 </head>
 </html>
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="utf-8"/>
	<title>Translate a Triangle</title>

	<body onload="main()">
	<canvas id="webgl" width="400" height="400">
	Please use a browser that supports "canvas"
	</canvas>
	</body>

	<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-utils.js"></script>
	<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/webgl-debug.js"></script>
	<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-utils.js"></script>
	<script src="https://rawgit.com/huningxin/webglbook_examples/master/lib/cuon-matrix.js"></script>
	<script type="text/javascript">
	// Shadow.js (c) 2012 matsuda and tanaka
	// Vertex shader program for generating a shadow map
	var SHADOW_VSHADER_SOURCE =
	'attribute vec4 a_Position;\n' +
	'uniform mat4 u_MvpMatrix;\n' +
	'void main() {\n' +
	' gl_Position = u_MvpMatrix * a_Position;\n' +
	'}\n';

	// Fragment shader program for generating a shadow map
	var SHADOW_FSHADER_SOURCE =
	'#ifdef GL_ES\n' +
	'precision mediump float;\n' +
	'#endif\n' +
	'void main() {\n' +
	' gl_FragColor = vec4(gl_FragCoord.z, 0.0, 0.0, 0.0);\n' + // Write the z-value in R
	'}\n';

	// Vertex shader program for regular drawing
	var VSHADER_SOURCE =
	'attribute vec4 a_Position;\n' +
	'attribute vec4 a_Color;\n' +
	'uniform mat4 u_MvpMatrix;\n' +
	'uniform mat4 u_MvpMatrixFromLight;\n' +
	'varying vec4 v_PositionFromLight;\n' +
	'varying vec4 v_Color;\n' +
	'void main() {\n' +
	' gl_Position = u_MvpMatrix * a_Position;\n' +
	' v_PositionFromLight = u_MvpMatrixFromLight * a_Position;\n' +
	' v_Color = a_Color;\n' +
	'}\n';

	// Fragment shader program for regular drawing
	var FSHADER_SOURCE =
	'#ifdef GL_ES\n' +
	'precision mediump float;\n' +
	'#endif\n' +
	'uniform sampler2D u_ShadowMap;\n' +
	'varying vec4 v_PositionFromLight;\n' +
	'varying vec4 v_Color;\n' +
	'void main() {\n' +
	' vec3 shadowCoord = (v_PositionFromLight.xyz/v_PositionFromLight.w)/2.0 + 0.5;\n' +
	' vec4 rgbaDepth = texture2D(u_ShadowMap, shadowCoord.xy);\n' +
	' float depth = rgbaDepth.r;\n' + // Retrieve the z-value from R
	' float visibility = (shadowCoord.z > depth + 0.005) ? 0.7 : 1.0;\n' +
	' gl_FragColor = vec4(v_Color.rgb * visibility, v_Color.a);\n' +
	'}\n';

	var OFFSCREEN_WIDTH = 2048, OFFSCREEN_HEIGHT = 2048;
	var LIGHT_X = 0, LIGHT_Y = 7, LIGHT_Z = 2; // Position of the light source

	function main() {
	// Retrieve <canvas> element
	var canvas = document.getElementById('webgl');

	// Get the rendering context for WebGL
	var gl = getWebGLContext(canvas);
	if (!gl) {
	console.log('Failed to get the rendering context for WebGL');
	return;
	}

	// Initialize shaders for generating a shadow map
	var shadowProgram = createProgram(gl, SHADOW_VSHADER_SOURCE, SHADOW_FSHADER_SOURCE);
	shadowProgram.a_Position = gl.getAttribLocation(shadowProgram, 'a_Position');
	shadowProgram.u_MvpMatrix = gl.getUniformLocation(shadowProgram, 'u_MvpMatrix');
	if (shadowProgram.a_Position < 0 \|\| !shadowProgram.u_MvpMatrix) {
	console.log('Failed to get the storage location of attribute or uniform variable from shadowProgram');
	return;
	}

	// Initialize shaders for regular drawing
	var normalProgram = createProgram(gl, VSHADER_SOURCE, FSHADER_SOURCE);
	normalProgram.a_Position = gl.getAttribLocation(normalProgram, 'a_Position');
	normalProgram.a_Color = gl.getAttribLocation(normalProgram, 'a_Color');
	normalProgram.u_MvpMatrix = gl.getUniformLocation(normalProgram, 'u_MvpMatrix');
	normalProgram.u_MvpMatrixFromLight = gl.getUniformLocation(normalProgram, 'u_MvpMatrixFromLight');
	normalProgram.u_ShadowMap = gl.getUniformLocation(normalProgram, 'u_ShadowMap');
	if (normalProgram.a_Position < 0 \|\| normalProgram.a_Color < 0 \|\| !normalProgram.u_MvpMatrix \|\|
	!normalProgram.u_MvpMatrixFromLight \|\| !normalProgram.u_ShadowMap) {
	console.log('Failed to get the storage location of attribute or uniform variable from normalProgram');
	return;
	}

	// Set the vertex information
	var triangle = initVertexBuffersForTriangle(gl);
	var plane = initVertexBuffersForPlane(gl);
	if (!triangle \|\| !plane) {
	console.log('Failed to set the vertex information');
	return;
	}

	// Initialize framebuffer object (FBO)
	var fbo = initFramebufferObject(gl);
	if (!fbo) {
	console.log('Failed to initialize frame buffer object');
	return;
	}
	gl.activeTexture(gl.TEXTURE0); // Set a texture object to the texture unit
	gl.bindTexture(gl.TEXTURE_2D, fbo.texture);

	// Set the clear color and enable the depth test
	gl.clearColor(0, 0, 0, 1);
	gl.enable(gl.DEPTH_TEST);

	var viewProjMatrixFromLight = new Matrix4(); // Prepare a view projection matrix for generating a shadow map
	viewProjMatrixFromLight.setPerspective(70.0, OFFSCREEN_WIDTH/OFFSCREEN_HEIGHT, 1.0, 100.0);
	viewProjMatrixFromLight.lookAt(LIGHT_X, LIGHT_Y, LIGHT_Z, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

	var viewProjMatrix = new Matrix4(); // Prepare a view projection matrix for regular drawing
	viewProjMatrix.setPerspective(45, canvas.width/canvas.height, 1.0, 100.0);
	viewProjMatrix.lookAt(0.0, 7.0, 9.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

	var currentAngle = 0.0; // Current rotation angle (degrees)
	var mvpMatrixFromLight_t = new Matrix4(); // A model view projection matrix from light source (for triangle)
	var mvpMatrixFromLight_p = new Matrix4(); // A model view projection matrix from light source (for plane)
	var tick = function() {
	currentAngle = animate(currentAngle);

	gl.bindFramebuffer(gl.FRAMEBUFFER, fbo); // Change the drawing destination to FBO
	gl.viewport(0, 0, OFFSCREEN_HEIGHT, OFFSCREEN_HEIGHT); // Set view port for FBO
	gl.clear(gl.COLOR_BUFFER_BIT \| gl.DEPTH_BUFFER_BIT); // Clear FBO

	gl.useProgram(shadowProgram); // Set shaders for generating a shadow map
	// Draw the triangle and the plane (for generating a shadow map)
	drawTriangle(gl, shadowProgram, triangle, currentAngle, viewProjMatrixFromLight);
	mvpMatrixFromLight_t.set(g_mvpMatrix); // Used later
	drawPlane(gl, shadowProgram, plane, viewProjMatrixFromLight);
	mvpMatrixFromLight_p.set(g_mvpMatrix); // Used later

	gl.bindFramebuffer(gl.FRAMEBUFFER, null); // Change the drawing destination to color buffer
	gl.viewport(0, 0, canvas.width, canvas.height);
	gl.clear(gl.COLOR_BUFFER_BIT \| gl.DEPTH_BUFFER_BIT); // Clear color and depth buffer

	gl.useProgram(normalProgram); // Set the shader for regular drawing
	gl.uniform1i(normalProgram.u_ShadowMap, 0); // Pass 0 because gl.TEXTURE0 is enabledする
	// Draw the triangle and plane ( for regular drawing)
	gl.uniformMatrix4fv(normalProgram.u_MvpMatrixFromLight, false, mvpMatrixFromLight_t.elements);
	drawTriangle(gl, normalProgram, triangle, currentAngle, viewProjMatrix);
	gl.uniformMatrix4fv(normalProgram.u_MvpMatrixFromLight, false, mvpMatrixFromLight_p.elements);
	drawPlane(gl, normalProgram, plane, viewProjMatrix);

	window.requestAnimationFrame(tick, canvas);
	};
	tick();
	}

	// Coordinate transformation matrix
	var g_modelMatrix = new Matrix4();
	var g_mvpMatrix = new Matrix4();
	function drawTriangle(gl, program, triangle, angle, viewProjMatrix) {
	// Set rotate angle to model matrix and draw triangle
	g_modelMatrix.setRotate(angle, 0, 1, 0);
	draw(gl, program, triangle, viewProjMatrix);
	}

	function drawPlane(gl, program, plane, viewProjMatrix) {
	// Set rotate angle to model matrix and draw plane
	g_modelMatrix.setRotate(-45, 0, 1, 1);
	draw(gl, program, plane, viewProjMatrix);
	}

	function draw(gl, program, o, viewProjMatrix) {
	initAttributeVariable(gl, program.a_Position, o.vertexBuffer);
	if (program.a_Color != undefined) // If a_Color is defined to attribute
	initAttributeVariable(gl, program.a_Color, o.colorBuffer);

	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, o.indexBuffer);

	// Calculate the model view project matrix and pass it to u_MvpMatrix
	g_mvpMatrix.set(viewProjMatrix);
	g_mvpMatrix.multiply(g_modelMatrix);
	gl.uniformMatrix4fv(program.u_MvpMatrix, false, g_mvpMatrix.elements);

	gl.drawElements(gl.TRIANGLES, o.numIndices, gl.UNSIGNED_BYTE, 0);
	}

	// Assign the buffer objects and enable the assignment
	function initAttributeVariable(gl, a_attribute, buffer) {
	gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
	gl.vertexAttribPointer(a_attribute, buffer.num, buffer.type, false, 0, 0);
	gl.enableVertexAttribArray(a_attribute);
	}

	function initVertexBuffersForPlane(gl) {
	// Create a plane
	// v1------v0
	// \| \|
	// \| \|
	// \| \|
	// v2------v3

	// Vertex coordinates
	var vertices = new Float32Array([
	3.0, -1.7, 2.5, -3.0, -1.7, 2.5, -3.0, -1.7, -2.5, 3.0, -1.7, -2.5 // v0-v1-v2-v3
	]);

	// Colors
	var colors = new Float32Array([
	1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0
	]);

	// Indices of the vertices
	var indices = new Uint8Array([0, 1, 2, 0, 2, 3]);

	var o = new Object(); // Utilize Object object to return multiple buffer objects together

	// Write vertex information to buffer object
	o.vertexBuffer = initArrayBufferForLaterUse(gl, vertices, 3, gl.FLOAT);
	o.colorBuffer = initArrayBufferForLaterUse(gl, colors, 3, gl.FLOAT);
	o.indexBuffer = initElementArrayBufferForLaterUse(gl, indices, gl.UNSIGNED_BYTE);
	if (!o.vertexBuffer \|\| !o.colorBuffer \|\| !o.indexBuffer) return null;

	o.numIndices = indices.length;

	// Unbind the buffer object
	gl.bindBuffer(gl.ARRAY_BUFFER, null);
	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

	return o;
	}

	function initVertexBuffersForTriangle(gl) {
	// Create a triangle
	// v2
	// / \|
	// / \|
	// / \|
	// v0----v1

	// Vertex coordinates
	var vertices = new Float32Array([-0.8, 3.5, 0.0, 0.8, 3.5, 0.0, 0.0, 3.5, 1.8]);
	// Colors
	var colors = new Float32Array([1.0, 0.5, 0.0, 1.0, 0.5, 0.0, 1.0, 0.0, 0.0]);
	// Indices of the vertices
	var indices = new Uint8Array([0, 1, 2]);

	var o = new Object(); // Utilize Object object to return multiple buffer objects together

	// Write vertex information to buffer object
	o.vertexBuffer = initArrayBufferForLaterUse(gl, vertices, 3, gl.FLOAT);
	o.colorBuffer = initArrayBufferForLaterUse(gl, colors, 3, gl.FLOAT);
	o.indexBuffer = initElementArrayBufferForLaterUse(gl, indices, gl.UNSIGNED_BYTE);
	if (!o.vertexBuffer \|\| !o.colorBuffer \|\| !o.indexBuffer) return null;

	o.numIndices = indices.length;

	// Unbind the buffer object
	gl.bindBuffer(gl.ARRAY_BUFFER, null);
	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, null);

	return o;
	}

	function initArrayBufferForLaterUse(gl, data, num, type) {
	// Create a buffer object
	var buffer = gl.createBuffer();
	if (!buffer) {
	console.log('Failed to create the buffer object');
	return null;
	}
	// Write date into the buffer object
	gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
	gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);

	// Store the necessary information to assign the object to the attribute variable later
	buffer.num = num;
	buffer.type = type;

	return buffer;
	}

	function initElementArrayBufferForLaterUse(gl, data, type) {
	// Create a buffer object
	var buffer = gl.createBuffer();
	if (!buffer) {
	console.log('Failed to create the buffer object');
	return null;
	}
	// Write date into the buffer object
	gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, buffer);
	gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, data, gl.STATIC_DRAW);

	buffer.type = type;

	return buffer;
	}

	function initFramebufferObject(gl) {
	var framebuffer, texture, depthBuffer;

	// Define the error handling function
	var error = function() {
	if (framebuffer) gl.deleteFramebuffer(framebuffer);
	if (texture) gl.deleteTexture(texture);
	if (depthBuffer) gl.deleteRenderbuffer(depthBuffer);
	return null;
	}

	// Create a framebuffer object (FBO)
	framebuffer = gl.createFramebuffer();
	if (!framebuffer) {
	console.log('Failed to create frame buffer object');
	return error();
	}

	// Create a texture object and set its size and parameters
	texture = gl.createTexture(); // Create a texture object
	if (!texture) {
	console.log('Failed to create texture object');
	return error();
	}
	gl.bindTexture(gl.TEXTURE_2D, texture);
	gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, OFFSCREEN_WIDTH, OFFSCREEN_HEIGHT, 0, gl.RGBA, gl.UNSIGNED_BYTE, null);
	gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR);

	// Create a renderbuffer object and Set its size and parameters
	depthBuffer = gl.createRenderbuffer(); // Create a renderbuffer object
	if (!depthBuffer) {
	console.log('Failed to create renderbuffer object');
	return error();
	}
	gl.bindRenderbuffer(gl.RENDERBUFFER, depthBuffer);
	gl.renderbufferStorage(gl.RENDERBUFFER, gl.DEPTH_COMPONENT16, OFFSCREEN_WIDTH, OFFSCREEN_HEIGHT);

	// Attach the texture and the renderbuffer object to the FBO
	gl.bindFramebuffer(gl.FRAMEBUFFER, framebuffer);
	gl.framebufferTexture2D(gl.FRAMEBUFFER, gl.COLOR_ATTACHMENT0, gl.TEXTURE_2D, texture, 0);
	gl.framebufferRenderbuffer(gl.FRAMEBUFFER, gl.DEPTH_ATTACHMENT, gl.RENDERBUFFER, depthBuffer);

	// Check if FBO is configured correctly
	var e = gl.checkFramebufferStatus(gl.FRAMEBUFFER);
	if (gl.FRAMEBUFFER_COMPLETE !== e) {
	console.log('Frame buffer object is incomplete: ' + e.toString());
	return error();
	}

	framebuffer.texture = texture; // keep the required object

	// Unbind the buffer object
	gl.bindFramebuffer(gl.FRAMEBUFFER, null);
	gl.bindTexture(gl.TEXTURE_2D, null);
	gl.bindRenderbuffer(gl.RENDERBUFFER, null);

	return framebuffer;
	}

	var ANGLE_STEP = 40; // The increments of rotation angle (degrees)

	var last = Date.now(); // Last time that this function was called
	function animate(angle) {
	var now = Date.now(); // Calculate the elapsed time
	var elapsed = now - last;
	last = now;
	// Update the current rotation angle (adjusted by the elapsed time)
	var newAngle = angle + (ANGLE_STEP * elapsed) / 1000.0;
	return newAngle % 360;
	}


	</script>
	</head>
	</html>