96 lines
2.4 KiB
JavaScript
96 lines
2.4 KiB
JavaScript
// ClickedPints.js (c) 2012 matsuda, 2022 Jonathon Doran
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// Note that this shader takes the position from the main
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// program, rather than hard-coding it.
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const vertex_shader = `
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attribute vec4 a_Position; // vertex-shader attribute
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void main()
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{
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gl_Position = a_Position;
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gl_PointSize = 25.0;
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} `;
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const fragment_shader = `
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void main()
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{
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gl_FragColor = vec4(1.0, 1.0, 0.0, 1.0);
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} `;
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function main()
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{
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// Retrieve <canvas> element
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var canvas = document.getElementById('webgl');
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// Get the rendering context for WebGL
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var gl = getWebGLContext(canvas);
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if (!gl)
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{
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console.log('Failed to get the rendering context for WebGL');
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return;
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}
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// Initialize shaders
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if (!initShaders(gl, vertex_shader, fragment_shader))
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{
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console.log('Failed to intialize shaders.');
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return;
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}
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// Get the storage location of a_Position
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// This is in video memory
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var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
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if (a_Position < 0)
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{
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console.log('Failed to get the storage location of a_Position');
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return;
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}
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// Register function (event handler) to be called on a mouse press
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canvas.onmousedown = function(ev){ click(ev, gl, canvas, a_Position); };
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// Specify the color for clearing <canvas>
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gl.clearColor(0.3, 0.3, 0.3, 1.0);
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// Clear <canvas>
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gl.clear(gl.COLOR_BUFFER_BIT);
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}
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// The array for the position of a mouse press:
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// Data is pushed onto this array, which resizes dynamically
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var g_points = [];
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function click(ev, gl, canvas, a_Position)
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{
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var x = ev.clientX; // x coordinate of a mouse pointer
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var y = ev.clientY; // y coordinate of a mouse pointer
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var rect = ev.target.getBoundingClientRect();
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// Coordinate conversion because canvas and WebGL have different
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// origins.
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x = ((x - rect.left) - canvas.width/2)/(canvas.width/2);
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y = (canvas.height/2 - (y - rect.top))/(canvas.height/2);
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// Store the coordinates to g_points array
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g_points.push(x);
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g_points.push(y);
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// Clear <canvas>
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gl.clear(gl.COLOR_BUFFER_BIT);
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// Upon each click, the canvas is cleared and all saved points
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// are redrawn. Each point has two values in the array (x, y).
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var len = g_points.length;
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for(var i = 0; i < len; i += 2)
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{
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// Pass the position of a point to a_Position variable
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gl.vertexAttrib3f(a_Position, g_points[i], g_points[i+1], 0.0);
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// Draw
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gl.drawArrays(gl.POINTS, 0, 1);
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}
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}
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