webgl-fundamentals/webgl/webgl-2d-rectangle-top-left.html at master · gfxfundamentals/webgl-fundamentals · GitHub

Name: webgl-fundamentals/webgl/webgl-2d-rectangle-top-left.html at master · gfxfundamentals/webgl-fundamentals · GitHub
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<!-- Licensed under a BSD license. See license.html for license -->
<!DOCTYPE html>
<html>
<head>
<metacharset="utf-8">
<metaname="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
<title>WebGL - 2D Rectangle Top Left</title>
<linktype="text/css" href="resources/webgl-tutorials.css" rel="stylesheet" />
</head>
<body>
<canvasid="c"></canvas>
</body>
<!--
for most samples webgl-utils only provides shader compiling/linking and
canvas resizing because why clutter the examples with code that's the same in every sample.
See https://webglfundamentals.org/webgl/lessons/webgl-boilerplate.html
and https://webglfundamentals.org/webgl/lessons/webgl-resizing-the-canvas.html
for webgl-utils, m3, m4, and webgl-lessons-ui.
-->
<scriptsrc="resources/webgl-utils.js"></script>
<!-- vertex shader -->
<scriptid="vertex-shader-2d" type="notjs">
attributevec4a_position;

uniformvec2u_resolution;

voidmain(){
// convert the position from pixels to 0.0 to 1.0
vec2 zeroToOne =a_position.xy/u_resolution;

// convert from 0->1 to 0->2
vec2zeroToTwo=zeroToOne*2.0;

// convert from 0->2 to -1->+1 (clipspace)
vec2clipSpace=zeroToTwo-1.0;

gl_Position=vec4(clipSpace*vec2(1,-1),0,1);
}
</script>
<!-- fragment shader -->
<scriptid="fragment-shader-2d" type="notjs">
precisionmediumpfloat;

voidmain(){
gl_FragColor=vec4(1,0,0.5,1);// return redish-purple
}
</script>
<script>
"use strict";

functionmain(){
// Get A WebGL context
varcanvas=document.querySelector("#c");
vargl=canvas.getContext("webgl");
if(!gl){
return;
}

// Use our boilerplate utils to compile the shaders and link into a program
varprogram=webglUtils.createProgramFromScripts(gl,["vertex-shader-2d","fragment-shader-2d"]);

// look up where the vertex data needs to go.
varpositionAttributeLocation=gl.getAttribLocation(program,"a_position");

// look up uniform locations
varresolutionUniformLocation=gl.getUniformLocation(program,"u_resolution");

// Create a buffer and put three 2d clip space points in it
varpositionBuffer=gl.createBuffer();

// Bind it to ARRAY_BUFFER (think of it as ARRAY_BUFFER = positionBuffer)
gl.bindBuffer(gl.ARRAY_BUFFER,positionBuffer);

varpositions=[
10,20,
80,20,
10,30,
10,30,
80,20,
80,30,
];
gl.bufferData(gl.ARRAY_BUFFER,newFloat32Array(positions),gl.STATIC_DRAW);

webglUtils.resizeCanvasToDisplaySize(gl.canvas);

// Tell WebGL how to convert from clip space to pixels
gl.viewport(0,0,gl.canvas.width,gl.canvas.height);

// Clear the canvas
gl.clearColor(0,0,0,0);
gl.clear(gl.COLOR_BUFFER_BIT);

// Tell it to use our program (pair of shaders)
gl.useProgram(program);

// Turn on the attribute
gl.enableVertexAttribArray(positionAttributeLocation);

// Bind the position buffer.
gl.bindBuffer(gl.ARRAY_BUFFER,positionBuffer);

// Tell the attribute how to get data out of positionBuffer (ARRAY_BUFFER)
varsize=2;// 2 components per iteration
vartype=gl.FLOAT;// the data is 32bit floats
varnormalize=false;// don't normalize the data
varstride=0;// 0 = move forward size * sizeof(type) each iteration to get the next position
varoffset=0;// start at the beginning of the buffer
gl.vertexAttribPointer(
positionAttributeLocation,size,type,normalize,stride,offset);

// set the resolution
gl.uniform2f(resolutionUniformLocation,gl.canvas.width,gl.canvas.height);

// draw
varprimitiveType=gl.TRIANGLES;
varoffset=0;
varcount=6;
gl.drawArrays(primitiveType,offset,count);
}

main();
</script>
</html>