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When I run the JavaScript/WebGL code below (please scroll down), I see the following warning message in my development console:
[.WebGLRenderingContext]
PERFORMANCE WARNING: Attribute 0 is disabled.
This has significant performance penalty
The code below successfully draws a white dot on the canvas. However, I want the warning to go away. What do I need to change in the code below to make it stop appearing?
The HTML:
<!DOCTYPE html>
<html>
<body>
<canvas id="canvas" width="100" height="100"></canvas>
</body>
</html>
The JavaScript:
var
VERTEX_SHADER_SOURCE = ""+
"void main() {"+
" gl_Position = vec4(0.0, 0.0, 0.0, 1.0);"+
" gl_PointSize = 10.0;"+
"}",
FRAGMENT_SHADER_SOURCE = ""+
"void main() {"+
" gl_FragColor = vec4(1.0, 1.0, 1.0, 1.0);"+
"}",
canvas = document.getElementById('canvas'),
gl = canvas.getContext('webgl'),
vertexShader = gl.createShader(gl.VERTEX_SHADER),
fragmentShader = gl.createShader(gl.FRAGMENT_SHADER),
shaderProgram = gl.createProgram();
// Compile the shaders.
gl.shaderSource(vertexShader, VERTEX_SHADER_SOURCE);
gl.compileShader(vertexShader);
gl.shaderSource(fragmentShader, FRAGMENT_SHADER_SOURCE);
gl.compileShader(fragmentShader);
// Create linked program.
gl.attachShader(shaderProgram, vertexShader);
gl.attachShader(shaderProgram, fragmentShader);
gl.linkProgram(shaderProgram);
gl.useProgram(shaderProgram);
// Clear the canvas.
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
// Draw the point.
gl.drawArrays(gl.POINTS, 0, 1);
This is a minimal, but complete example, so I'm looking for an answer that tells me specifically what to change. Here is a JSFiddle of the case. I'm running this in Chrome 30.0.1599.101 (on OS X 10.8.5).
978
OpenGL requires attribute zero to be enabled otherwise it will not render anything. On the other hand OpenGL ES 2.0 on which WebGL is based does not. So, to emulate OpenGL ES 2.0 on top of OpenGL if you don't enable attribute 0 the browser has to make a buffer for you large enough for the number of vertices you've requested to be drawn, fill it with the correct value (see gl.vertexAttrib), attach it to attribute zero, and enable it.
It does all this behind the scenes but it's important for you to know that it takes time to create and fill that buffer. There are optimizations the browser can make but in the general case, if you were to assume you were running on OpenGL ES 2.0 and used attribute zero as a constant like you are supposed to be able to do, without the warning you'd have no idea of the work the browser is doing on your behalf to emulate that feature of OpenGL ES 2.0 that is different from OpenGL.
In your particular case the warning doesn't have much meaning. It looks like you are only drawing a single point. But it would not be easy for the browser to figure that out so it just warns you anytime you draw and attribute 0 is not enabled.
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