《The Book of Shaders》：Shader入门指南

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《着色器之书》是一本深入浅出的Fragment Shaders入门指南，由Patricio Gonzalez Vivo和Jen Lowe合著。本书旨在帮助读者理解并掌握这一复杂但强大的图形编程工具。书中内容包括但不限于以下几个核心知识点： 1. **介绍**：这本书面向的是对图形编程感兴趣的初学者，无论他们是在Unity、Three.js、Processing或openFrameworks等平台工作。作者首先解释了什么是Fragment Shaders，它们在图形渲染中的作用，以及为何它们在性能上具有优势。 2. **入门**： - **什么是Fragment Shader**：这部分详细介绍了片段着色器的概念，即负责处理像素级别的颜色和光照计算的代码。 - **为什么Shader快速**：通过解释GPU并行处理的优势和Shader在硬件上的优化，阐述了Shader如何加速渲染过程。 - **GLSL**：作为标准的着色器语言，GLSL是学习者必须了解的基础，这里会介绍其语法和基本概念。 - **Shader痛苦的原因**：探讨了Shader编程的挑战，如学习曲线陡峭和潜在的精度问题，但同时也强调了其带来的创造可能性。 3. **Hello World和基础设置**： - **HelloWorld示例**：给出了一个简单的入门项目，展示了如何编写并运行第一个基本的Fragment Shader。 - ** uniforms**：讲解了如何在Shader中传递和使用外部变量，如常量、纹理坐标等。 - **gl_FragCoord**：介绍了一个重要的内置变量，用于访问当前正在处理的像素坐标。 4. **算法绘图**： - **形状函数**：介绍了一系列基础的数学函数，如步进函数、平滑步进函数，用于创建复杂的几何形状。 - **颜色混合**：涵盖了颜色混合的基本操作，如线性混合和渐变效果。 - **颜色空间**：讲解了HSB色彩模型，以及在极坐标下使用HSB的技巧。 5. **形状生成**： - **矩形、圆形**：展示如何用Shader生成几何形状。 - **距离场**：解释了距离场的概念，用于制作模糊边缘效果，并探讨其实用性质。 - **矩阵与变换**：介绍了二维矩阵用于变换几何形状，包括平移、旋转和缩放，以及在YUV色彩空间的应用。通过这些章节，读者能够逐步建立起对Fragment Shader的理解，从基础知识到实际应用，为他们在游戏开发、视觉艺术和实时图形处理领域打下坚实的基础。无论是为了职业发展还是个人兴趣，这都是一本不可或缺的参考书籍。

2 Getting started

6. Float types are vital in shaders, so the level of precision is crucial. Lower precision

means faster rendering, but at the cost of quality. You can be picky and specify

the precision of each variable that uses oating point. In the rst line (precision

mediump float;) we are setting all oats to medium precision. But we can choose

to set them to low (precision lowp float;) or high (precision highp float;).

7. The last, and maybe most important, detail is that GLSL specs don’t guarantee

that variables will be automatically casted. What does that mean? Manufacturers

have dierent approaches to accelerate graphic card processes but they are forced

to guarantee minimum specs. Automatic casting is not one of them. In our “hello

world!” example vec4 has oating point precision and for that it expects to be

assigned with floats. If you want to make good consistent code and not spend

hours debugging white screens, get used to putting the point ( . ) in your oats.

This kind of code will not always work:

void main() {

gl_FragColor = vec4(1,0,0,1); // ERROR

}

Now that we’ve described the most relevant elements of our “hello world!” program, it’s

time to click on the code block and start challenging all that we’ve learned. You will

note that on errors, the program will fail to compile, showing a white screen. There are

some interesting things to try, for example:

• Try replacing the oats with integers, your graphic card may or may not tolerate

this behavior.

• Try commenting out line 6 and not assigning any pixel value to the function.

• Try making a separate function that returns a specic color and use it inside

main(). As a hint, here is the code for a function that returns a red color:

vec4 red(){

return vec4(1.0,0.0,0.0,1.0);

}

• There are multiple ways of constructing vec4 types, try to discover other ways.

The following is one of them:

vec4 color = vec4(vec3(1.0,0.0,1.0),1.0);

Although this example isn’t very exciting, it is the most basic example - we are changing

all the pixels inside the canvas to the same exact color. In the following chapter we will

see how to change the pixel colors by using two types of input: space (the place of the

pixel on the screen) and time (the number of seconds since the page was loaded).

2.6 Uniforms

So far we have seen how the GPU manages large numbers of parallel threads, each one

responsible for assigning the color to a fraction of the total image. Although each parallel

thread is blind to the others, we need to be able to send some inputs from the CPU to

all the threads. Because of the architecture of the graphic card those inputs are going

to be equal (uniform) to all the threads and necessarily set as read only. In other words,

each thread receives the same data which it can read but cannot change.

These inputs are call uniform and come in most of the supported types: float, vec2,

vec3, vec4, mat2, mat3, mat4, sampler2D and samplerCube. Uniforms are dened with

the corresponding type at the top of the shader right after assigning the default oating

point precision.

#ifdef GL_ES

precision mediump float;

#endif

uniform vec2 u_resolution; // Canvas size (width,height)

uniform vec2 u_mouse; // mouse position in screen pixels

uniform float u_time; // Time in seconds since load

You can picture the uniforms like little bridges between the CPU and the GPU. The

names will vary from implementation to implementation but in this series of examples

I’m always passing: u_time (time in seconds since the shader started), u_resolution

(billboard size where the shader is being drawn) and u_mouse (mouse position inside the

billboard in pixels). I’m following the convention of putting u_ before the uniform name

to be explicit about the nature of this variable but you will nd all kinds of names for

uniforms. For example ShaderToy.com uses the same uniforms but with the following

names:

uniform vec3 iResolution; // viewport resolution (in pixels)

uniform vec4 iMouse; // mouse pixel coords. xy: current, zw: click

uniform float iGlobalTime; // shader playback time (in seconds)

Enough talking, let’s see the uniforms in action. In the following code we use u_time -

the number of seconds since the shader started running - together with a sine function

to animate the transition of the amount of red in the billboard.

#ifdef GL_ES

precision mediump float;

#endif

uniform float u_time;

void main() {

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