为什么每次我在 p5js 中调用我的 glsl 着色器时我的纹理坐标都会反转？
Why my texture coordinates are inverted each time I call my glsl shader in p5js?
我正在尝试将 glsl 着色器与 p5js 一起使用来创建类似生活游戏的模拟。为此，我想创建一个着色器，它将纹理视为统一的，并根据之前的纹理绘制新纹理。在下一次迭代中，这个新纹理将用作统一纹理，这应该允许我按照公开的想法创建一个模拟 here。我对 p5.js 很有经验，但我对着色器编程完全陌生，所以我可能遗漏了一些东西。
现在我的代码尽可能简单：
- 在
preload() 函数中，我使用 createImage() 函数创建了一个纹理，并将一些像素设置为白色，其他像素设置为黑色。
- 在
setup() 函数中我第一次使用这个纹理来 运行 着色器来创建一个新的纹理。我还定期为 运行 着色器设置一个计时器，并将结果绘制在缓冲区中。
- 在
draw() 函数中，我在 canvas 中绘制缓冲区。
- 为了简单起见，我保持 canvas 和纹理大小相同。
我的问题是在某些时候我的代码中的 y 坐标似乎颠倒了，我不明白为什么。 我的理解是我的代码应该显示静止图像，但每次我 运行 着色器图像都会反转。这就是我的意思：
我不确定我的问题是来自于我如何使用 glsl 还是我如何使用 p5 或两者兼而有之。有人可以向我解释一下这种奇怪的 y 反转是从哪里来的吗？
这是我的最小可重现示例（也在 p5 编辑器 here 中）：
草图文件：
const sketch = (p5) => {
const D = 100;
let initialTexture;
p5.preload = () => {
// Create the initial image
initialTexture = p5.createImage(D, D);
initialTexture.loadPixels();
for (let i = 0; i < initialTexture.width; i++) {
for (let j = 0; j < initialTexture.height; j++) {
const alive = i === j || i === 10 || j === 40;
const color = p5.color(250, 250, 250, alive ? 250 : 0);
initialTexture.set(i, j, color);
}
}
initialTexture.updatePixels();
// Initialize the shader
shader = p5.loadShader('uniform.vert', 'test.frag');
};
p5.setup = () => {
const canvas = p5.createCanvas(D, D, p5.WEBGL);
canvas.parent('canvasDiv');
// Create the buffer the shader will draw on
graphics = p5.createGraphics(D, D, p5.WEBGL);
graphics.shader(shader);
/*
* Initial step to setup the initial texture
*/
// Used to normalize the frag coordinates
shader.setUniform('u_resolution', [p5.width, p5.height]);
// First state of the simulation
shader.setUniform('u_texture', initialTexture);
graphics.rect(0, 0, p5.width, p5.height);
// Call the shader each time interval
setInterval(updateSimulation, 1009);
};
const updateSimulation = () => {
// Use the previous state as a texture
shader.setUniform('u_texture', graphics);
graphics.rect(0, 0, p5.width, p5.height);
};
p5.draw = () => {
p5.background(0);
// Use the buffer on the canvas
p5.image(graphics, -p5.width / 2, -p5.height / 2);
};
};
new p5(sketch);
片段着色器，目前只获取纹理的颜色并重新使用它（我尝试使用 st 而不是 uv 无济于事）：
precision highp float;
uniform vec2 u_resolution;
uniform sampler2D u_texture;
// grab texcoords from vert shader
varying vec2 vTexCoord;
void main() {
// Normalize the position between 0 and 1
vec2 st = gl_FragCoord.xy/u_resolution.xy;
// Get the texture coordinate from the vertex shader
vec2 uv = vTexCoord;
// Get the color at the texture coordinate
vec4 c = texture2D(u_texture, uv);
// Reuse the same color
gl_FragColor = c;
}
我从 an example 获取的顶点着色器除了传递坐标外什么都不做：
/*
* vert file and comments from adam ferriss https://github.com/aferriss/p5jsShaderExamples with additional comments from Louise Lessel
*/
precision highp float;
// This “vec3 aPosition” is a built in shader functionality. You must keep that naming.
// It automatically gets the position of every vertex on your canvas
attribute vec3 aPosition;
attribute vec2 aTexCoord;
varying vec2 vTexCoord;
// We always must do at least one thing in the vertex shader:
// tell the pixel where on the screen it lives:
void main() {
// copy the texcoords
vTexCoord = aTexCoord;
// copy the position data into a vec4, using 1.0 as the w component
vec4 positionVec4 = vec4(aPosition, 1.0);
positionVec4.xy = positionVec4.xy * 2.0 - 1.0;
// Send the vertex information on to the fragment shader
// this is done automatically, as long as you put it into the built in shader function “gl_Position”
gl_Position = positionVec4;
}
长话短说：用 p5.js 绘制的矩形或平面的纹理坐标是左下角的 (0, 0) 和右上角的 (1, 1)，其中从纹理中采样值的坐标系是 top 左侧的 (0, 0) 和 bottom 右侧的 (1, 1)。您可以通过在片段着色器中注释掉颜色采样代码并使用以下内容来验证这一点：
float val = (uv.x + uv.y) / 2.0;
gl_FragColor = vec4(val, val, val, 1.0);
正如您从结果图像中看到的那样：
值 (0 + 0) / 2 导致左下角为黑色，(1 + 1) / 2 导致右上角为白色。
因此，要对纹理的正确部分进行采样，您只需翻转 uv 向量的 y 分量：
texture2D(u_texture, vec2(uv.x, 1.0 - uv.y));
const sketch = (p5) => {
const D = 200;
let initialTexture;
p5.preload = () => {
// This doesn't actually need to go in preload
// Create the initial image
initialTexture = p5.createImage(D, D);
initialTexture.loadPixels();
for (let i = 0; i < initialTexture.width; i++) {
for (let j = 0; j < initialTexture.height; j++) {
// draw a big checkerboard
const alive = (p5.round(i / 10) + p5.round(j / 10)) % 2 == 0;
const color = alive ? p5.color('white') : p5.color(150, p5.map(j, 0, D, 50, 200), p5.map(i, 0, D, 50, 200));
initialTexture.set(i, j, color);
}
}
initialTexture.updatePixels();
};
p5.setup = () => {
const canvas = p5.createCanvas(D, D, p5.WEBGL);
// Create the buffer the shader will draw on
graphics = p5.createGraphics(D, D, p5.WEBGL);
// Initialize the shader
shader = graphics.createShader(vert, frag);
graphics.shader(shader);
/*
* Initial step to setup the initial texture
*/
// Used to normalize the frag coordinates
shader.setUniform('u_resolution', [p5.width, p5.height]);
// First state of the simulation
shader.setUniform('u_texture', initialTexture);
graphics.rect(0, 0, p5.width, p5.height);
// Call the shader each time interval
setInterval(updateSimulation, 100);
};
const updateSimulation = () => {
// Use the previous state as a texture
shader.setUniform('u_texture', graphics);
graphics.rect(0, 0, p5.width, p5.height);
};
p5.draw = () => {
p5.background(0);
// Use the buffer on the canvas
p5.texture(graphics);
p5.rect(-p5.width / 2, -p5.height / 2, p5.width, p5.height);
};
const frag = `
precision highp float;
uniform vec2 u_resolution;
uniform sampler2D u_texture;
// grab texcoords from vert shader
varying vec2 vTexCoord;
varying vec2 vPos;
void main() {
// Get the texture coordinate from the vertex shader
vec2 uv = vTexCoord;
gl_FragColor = texture2D(u_texture, vec2(uv.x, 1.0 - uv.y));
//// For debugging uv coordinate orientation
// float val = (uv.x + uv.y) / 2.0;
// gl_FragColor = vec4(val, val, val, 1.0);
}
`;
const vert = `
/*
* vert file and comments from adam ferriss https://github.com/aferriss/p5jsShaderExamples with additional comments from Louise Lessel
*/
precision highp float;
// This “vec3 aPosition” is a built in shader functionality. You must keep that naming.
// It automatically gets the position of every vertex on your canvas
attribute vec3 aPosition;
attribute vec2 aTexCoord;
varying vec2 vTexCoord;
// We always must do at least one thing in the vertex shader:
// tell the pixel where on the screen it lives:
void main() {
// copy the texcoords
vTexCoord = aTexCoord;
// copy the position data into a vec4, using 1.0 as the w component
vec4 positionVec4 = vec4(aPosition, 1.0);
// This maps positions 0..1 to -1..1
positionVec4.xy = positionVec4.xy * 2.0 - 1.0;
// Send the vertex information on to the fragment shader
// this is done automatically, as long as you put it into the built in shader function “gl_Position”
gl_Position = positionVec4;
}`;
};
new p5(sketch);
<script src="https://cdn.jsdelivr.net/npm/p5@1.3.1/lib/p5.js"></script>
我正在尝试将 glsl 着色器与 p5js 一起使用来创建类似生活游戏的模拟。为此，我想创建一个着色器，它将纹理视为统一的，并根据之前的纹理绘制新纹理。在下一次迭代中，这个新纹理将用作统一纹理，这应该允许我按照公开的想法创建一个模拟 here。我对 p5.js 很有经验，但我对着色器编程完全陌生，所以我可能遗漏了一些东西。
现在我的代码尽可能简单：
- 在
preload()函数中，我使用createImage()函数创建了一个纹理，并将一些像素设置为白色，其他像素设置为黑色。 - 在
setup()函数中我第一次使用这个纹理来 运行 着色器来创建一个新的纹理。我还定期为 运行 着色器设置一个计时器，并将结果绘制在缓冲区中。 - 在
draw()函数中，我在 canvas 中绘制缓冲区。 - 为了简单起见，我保持 canvas 和纹理大小相同。
我的问题是在某些时候我的代码中的 y 坐标似乎颠倒了，我不明白为什么。 我的理解是我的代码应该显示静止图像，但每次我 运行 着色器图像都会反转。这就是我的意思：
我不确定我的问题是来自于我如何使用 glsl 还是我如何使用 p5 或两者兼而有之。有人可以向我解释一下这种奇怪的 y 反转是从哪里来的吗？
这是我的最小可重现示例（也在 p5 编辑器 here 中）：
草图文件：
const sketch = (p5) => {
const D = 100;
let initialTexture;
p5.preload = () => {
// Create the initial image
initialTexture = p5.createImage(D, D);
initialTexture.loadPixels();
for (let i = 0; i < initialTexture.width; i++) {
for (let j = 0; j < initialTexture.height; j++) {
const alive = i === j || i === 10 || j === 40;
const color = p5.color(250, 250, 250, alive ? 250 : 0);
initialTexture.set(i, j, color);
}
}
initialTexture.updatePixels();
// Initialize the shader
shader = p5.loadShader('uniform.vert', 'test.frag');
};
p5.setup = () => {
const canvas = p5.createCanvas(D, D, p5.WEBGL);
canvas.parent('canvasDiv');
// Create the buffer the shader will draw on
graphics = p5.createGraphics(D, D, p5.WEBGL);
graphics.shader(shader);
/*
* Initial step to setup the initial texture
*/
// Used to normalize the frag coordinates
shader.setUniform('u_resolution', [p5.width, p5.height]);
// First state of the simulation
shader.setUniform('u_texture', initialTexture);
graphics.rect(0, 0, p5.width, p5.height);
// Call the shader each time interval
setInterval(updateSimulation, 1009);
};
const updateSimulation = () => {
// Use the previous state as a texture
shader.setUniform('u_texture', graphics);
graphics.rect(0, 0, p5.width, p5.height);
};
p5.draw = () => {
p5.background(0);
// Use the buffer on the canvas
p5.image(graphics, -p5.width / 2, -p5.height / 2);
};
};
new p5(sketch);
片段着色器，目前只获取纹理的颜色并重新使用它（我尝试使用 st 而不是 uv 无济于事）：
precision highp float;
uniform vec2 u_resolution;
uniform sampler2D u_texture;
// grab texcoords from vert shader
varying vec2 vTexCoord;
void main() {
// Normalize the position between 0 and 1
vec2 st = gl_FragCoord.xy/u_resolution.xy;
// Get the texture coordinate from the vertex shader
vec2 uv = vTexCoord;
// Get the color at the texture coordinate
vec4 c = texture2D(u_texture, uv);
// Reuse the same color
gl_FragColor = c;
}
我从 an example 获取的顶点着色器除了传递坐标外什么都不做：
/*
* vert file and comments from adam ferriss https://github.com/aferriss/p5jsShaderExamples with additional comments from Louise Lessel
*/
precision highp float;
// This “vec3 aPosition” is a built in shader functionality. You must keep that naming.
// It automatically gets the position of every vertex on your canvas
attribute vec3 aPosition;
attribute vec2 aTexCoord;
varying vec2 vTexCoord;
// We always must do at least one thing in the vertex shader:
// tell the pixel where on the screen it lives:
void main() {
// copy the texcoords
vTexCoord = aTexCoord;
// copy the position data into a vec4, using 1.0 as the w component
vec4 positionVec4 = vec4(aPosition, 1.0);
positionVec4.xy = positionVec4.xy * 2.0 - 1.0;
// Send the vertex information on to the fragment shader
// this is done automatically, as long as you put it into the built in shader function “gl_Position”
gl_Position = positionVec4;
}
长话短说：用 p5.js 绘制的矩形或平面的纹理坐标是左下角的 (0, 0) 和右上角的 (1, 1)，其中从纹理中采样值的坐标系是 top 左侧的 (0, 0) 和 bottom 右侧的 (1, 1)。您可以通过在片段着色器中注释掉颜色采样代码并使用以下内容来验证这一点：
float val = (uv.x + uv.y) / 2.0;
gl_FragColor = vec4(val, val, val, 1.0);
正如您从结果图像中看到的那样：
值 (0 + 0) / 2 导致左下角为黑色，(1 + 1) / 2 导致右上角为白色。
因此，要对纹理的正确部分进行采样，您只需翻转 uv 向量的 y 分量：
texture2D(u_texture, vec2(uv.x, 1.0 - uv.y));
const sketch = (p5) => {
const D = 200;
let initialTexture;
p5.preload = () => {
// This doesn't actually need to go in preload
// Create the initial image
initialTexture = p5.createImage(D, D);
initialTexture.loadPixels();
for (let i = 0; i < initialTexture.width; i++) {
for (let j = 0; j < initialTexture.height; j++) {
// draw a big checkerboard
const alive = (p5.round(i / 10) + p5.round(j / 10)) % 2 == 0;
const color = alive ? p5.color('white') : p5.color(150, p5.map(j, 0, D, 50, 200), p5.map(i, 0, D, 50, 200));
initialTexture.set(i, j, color);
}
}
initialTexture.updatePixels();
};
p5.setup = () => {
const canvas = p5.createCanvas(D, D, p5.WEBGL);
// Create the buffer the shader will draw on
graphics = p5.createGraphics(D, D, p5.WEBGL);
// Initialize the shader
shader = graphics.createShader(vert, frag);
graphics.shader(shader);
/*
* Initial step to setup the initial texture
*/
// Used to normalize the frag coordinates
shader.setUniform('u_resolution', [p5.width, p5.height]);
// First state of the simulation
shader.setUniform('u_texture', initialTexture);
graphics.rect(0, 0, p5.width, p5.height);
// Call the shader each time interval
setInterval(updateSimulation, 100);
};
const updateSimulation = () => {
// Use the previous state as a texture
shader.setUniform('u_texture', graphics);
graphics.rect(0, 0, p5.width, p5.height);
};
p5.draw = () => {
p5.background(0);
// Use the buffer on the canvas
p5.texture(graphics);
p5.rect(-p5.width / 2, -p5.height / 2, p5.width, p5.height);
};
const frag = `
precision highp float;
uniform vec2 u_resolution;
uniform sampler2D u_texture;
// grab texcoords from vert shader
varying vec2 vTexCoord;
varying vec2 vPos;
void main() {
// Get the texture coordinate from the vertex shader
vec2 uv = vTexCoord;
gl_FragColor = texture2D(u_texture, vec2(uv.x, 1.0 - uv.y));
//// For debugging uv coordinate orientation
// float val = (uv.x + uv.y) / 2.0;
// gl_FragColor = vec4(val, val, val, 1.0);
}
`;
const vert = `
/*
* vert file and comments from adam ferriss https://github.com/aferriss/p5jsShaderExamples with additional comments from Louise Lessel
*/
precision highp float;
// This “vec3 aPosition” is a built in shader functionality. You must keep that naming.
// It automatically gets the position of every vertex on your canvas
attribute vec3 aPosition;
attribute vec2 aTexCoord;
varying vec2 vTexCoord;
// We always must do at least one thing in the vertex shader:
// tell the pixel where on the screen it lives:
void main() {
// copy the texcoords
vTexCoord = aTexCoord;
// copy the position data into a vec4, using 1.0 as the w component
vec4 positionVec4 = vec4(aPosition, 1.0);
// This maps positions 0..1 to -1..1
positionVec4.xy = positionVec4.xy * 2.0 - 1.0;
// Send the vertex information on to the fragment shader
// this is done automatically, as long as you put it into the built in shader function “gl_Position”
gl_Position = positionVec4;
}`;
};
new p5(sketch);
<script src="https://cdn.jsdelivr.net/npm/p5@1.3.1/lib/p5.js"></script>