缩放
1 )原理
-
缩放可以理解为对向量长度的改变,或者对向量坐标分量的同步缩放
-
如下图,比如
-
让向量OA 收缩到点B的位置,也就是从OA变成OB,缩放了一半
2 )公式
在着色器中缩放
1 )核心代码
-
可以对gl_Position 的x、y、z依次缩放
<script id="vertexShader" type="x-shader/x-vertex">
attribute vec4 a_Position;
float scale = 1.2; // 注意这里声明了浮点型,一点要用浮点数,否则会导致 UseProgram: program not valid 的警告
void main() {
gl_Position.x = a_Position.x * scale;
gl_Position.y = a_Position.y * scale;
gl_Position.z = a_Position.z * scale;
gl_Position.w = 1.0; // 注意 w 的值,默认1.0
}
</script>
-
也可以从a_Position中抽离出由x、y、z组成的三维向量,对其进行一次性缩放
<script id="vertexShader" type="x-shader/x-vertex">
attribute vec4 a_Position;
float scale = 1.2;
void main() {
gl_Position = vec4(vec3(a_Position) * scale, 1.0);
}
</script>
2 )完整代码
<canvas id="canvas"></canvas>
<script id="vertexShader" type="x-shader/x-vertex">
attribute vec4 a_Position;
float scale = 1.0;
void main() {
gl_Position = vec4(vec3(a_Position) * scale, 1.0);
}
</script>
<script id="fragmentShader" type="x-shader/x-fragment">
void main(){
gl_FragColor = vec4(1.0, 1.0, 0.0, 1.0);
}
</script>
<script type="module">
import { initShaders } from './utils.js';
const canvas = document.getElementById('canvas');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
const gl = canvas.getContext('webgl');
const vsSource = document.getElementById('vertexShader').innerText;
const fsSource = document.getElementById('fragmentShader').innerText;
initShaders(gl, vsSource, fsSource);
const vertices = new Float32Array([
0.0, 0.1,
-0.1, -0.1,
0.1, -0.1
])
const vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
const a_Position = gl.getAttribLocation(gl.program, 'a_Position');
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_Position);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, 3);
</script>
用js缩放图形
1 )核心代码
-
同样的我们也可以把缩放系数暴露给js,通过js 缩放图形
-
建立uniform变量
<script id="vertexShader" type="x-shader/x-vertex">
attribute vec4 a_Position;
uniform float u_Scale;
void main() {
gl_Position = vec4(vec3(a_Position) * u_Scale, 1.0);
}
</script>
-
使用js获取并修改uniform 变量
const u_Scale = gl.getUniformLocation(gl.program, 'u_Scale')
gl.uniform1f(u_Scale, 1.0)
-
添加动画让其动起来
let angle = 0
!(function animate() {
angle += 0.05;
const scale = Math.sin(n) + 1; // 借助三角函数正弦进行缩放 (-1, 1) + 1 => (0, 2)
gl.uniform1f(u_Scale, scale);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, 3);
requestAnimationFrame(animate)
})()
2 )完整代码
<canvas id="canvas"></canvas>
<script id="vertexShader" type="x-shader/x-vertex">
attribute vec4 a_Position;
uniform float u_Scale;
void main() {
gl_Position = vec4(vec3(a_Position) * u_Scale, 1.0);
}
</script>
<script id="fragmentShader" type="x-shader/x-fragment">
void main() {
gl_FragColor = vec4(1.0,1.0,0.0,1.0);
}
</script>
<script type="module">
import { initShaders } from './utils.js';
const canvas = document.getElementById('canvas');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
const gl = canvas.getContext('webgl');
const vsSource = document.getElementById('vertexShader').innerText;
const fsSource = document.getElementById('fragmentShader').innerText;
initShaders(gl, vsSource, fsSource);
const vertices = new Float32Array([
0.0, 0.1,
-0.1, -0.1,
0.1, -0.1
])
const vertexBuffer = gl.createBuffer();
gl.bindBuffer(gl.ARRAY_BUFFER, vertexBuffer);
gl.bufferData(gl.ARRAY_BUFFER, vertices, gl.STATIC_DRAW);
const a_Position = gl.getAttribLocation(gl.program, 'a_Position');
gl.vertexAttribPointer(a_Position, 2, gl.FLOAT, false, 0, 0);
gl.enableVertexAttribArray(a_Position);
const u_Scale = gl.getUniformLocation(gl.program, 'u_Scale')
gl.uniform1f(u_Scale, 1);
gl.clearColor(0.0, 0.0, 0.0, 1.0);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, 3);
let angle = 0;
!(function animate() {
angle += 0.05;
const scale = Math.sin(angle) + 1;
gl.uniform1f(u_Scale, scale);
gl.clear(gl.COLOR_BUFFER_BIT);
gl.drawArrays(gl.TRIANGLES, 0, 3);
requestAnimationFrame(animate);
})()
</script>