webgl

一个三角形

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var canvas = document.getElementById("webgl");
var gl = canvas.getContext("webgl");

var vertexShaderSource = `
attribute vec4 a_position;
void main() {
gl_Position = a_position;
}
`;
var fragmentShaderSource = `
void main() {
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}
`;

var vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, vertexShaderSource);
gl.compileShader(vertexShader);

var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, fragmentShaderSource);
gl.compileShader(fragmentShader);

var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
gl.useProgram(program);

var a_position = gl.getAttribLocation(program, "a_position");
var data = new Float32Array([
  0.0, 0.5,
  -0.5, -0.5,
  0.5, -0.5
]);

var buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
gl.vertexAttribPointer(a_position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_position);
gl.drawArrays(gl.TRIANGLES, 0, 3);

void gl.drawArrays(mode, first, count);

  • gl.POINTS: Draws a single dot.
  • gl.LINE_STRIP: Draws a straight line to the next vertex.
  • gl.LINE_LOOP: Draws a straight line to the next vertex, and connects the last vertex back to the first.
  • gl.LINES: Draws a line between a pair of vertices.
  • gl.TRIANGLE_STRIP
  • gl.TRIANGLE_FAN
  • gl.TRIANGLES: Draws a triangle for a group of three vertices.

image-20210909202415631

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var canvas = document.getElementById("webgl2");
var gl = canvas.getContext("webgl");

var vertexShaderSource = `
attribute vec4 a_position;
void main() {
gl_Position = a_position;
gl_PointSize = 10.0;
}
`;
var fragmentShaderSource = `
void main() {
gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}
`;

var vertexShader = gl.createShader(gl.VERTEX_SHADER);
gl.shaderSource(vertexShader, vertexShaderSource);
gl.compileShader(vertexShader);

var fragmentShader = gl.createShader(gl.FRAGMENT_SHADER);
gl.shaderSource(fragmentShader, fragmentShaderSource);
gl.compileShader(fragmentShader);

var program = gl.createProgram();
gl.attachShader(program, vertexShader);
gl.attachShader(program, fragmentShader);
gl.linkProgram(program);
gl.useProgram(program);

var a_position = gl.getAttribLocation(program, "a_position");
var data = new Float32Array([
0.0, 0.5,
-0.5, -0.5,
0.5, -0.5
]);

var buffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, buffer);
gl.bufferData(gl.ARRAY_BUFFER, data, gl.STATIC_DRAW);
gl.vertexAttribPointer(a_position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_position);

gl.drawArrays(gl.POINTS, 0, 3);

//change color
fragmentShaderSource = `
void main() {
gl_FragColor = vec4(1.0, 1.0, 0.0, 1.0);
}
`;
gl.shaderSource(fragmentShader, fragmentShaderSource);
gl.compileShader(fragmentShader);
gl.attachShader(program, fragmentShader);

//translate position.y
vertexShaderSource = `
attribute vec4 a_position;
void main() {
gl_Position = a_position+vec4(0.0, 0.2, 0.0, 0.0);
gl_PointSize = 10.0;
}
`;
gl.shaderSource(vertexShader, vertexShaderSource);
gl.compileShader(vertexShader);
gl.attachShader(program, vertexShader);

gl.linkProgram(program);
gl.useProgram(program);

gl.drawArrays(gl.LINE_LOOP, 0, 3);

image-20210909194809748