CG: Text-Based Shaders
Bairui Su · Created 2025-09-14 · ASCII Art
/**
* ============================================================================
* = Computer Graphics: Text-Based Shaders =
* ============================================================================
*
* This tutorial introduces fundamental concepts of computer graphics through
* text-based shader implementations in Recho.
*
* I'm taking Prof. Ken Perlin's Computer Graphics course this semester. In the
* second lecture, it's fascinating to see him creating impressive visual
* effects with GPU-based fragment shaders.
*
* However, I find it challenging for beginners to set up WebGL and write GLSL
* code. Therefore, I'm creating text-based shader implementations in Recho to
* make computer graphics more accessible to beginners.
*
* > You don't have to be familiar with Canvas, WebGL, or GLSL. Only basic
* > JavaScript knowledge and some basic vector operations are required.
*
* After reading this, you will be able to create the following rotating sphere
* with diffuse reflection model and ambient light!
*/
//➜
//➜ +=~~~---::::....:
//➜ *+==~~---::::..........
//➜ #**++==~~---::::..... ..
//➜ %#*++===~~---::::..... .
//➜ %%##*+++==~~~---::::...... ..
//➜ %%%##**++===~~----::::....... ..:
//➜ %%%%##**+++==~~~~---:::::.............:
//➜ %%%%%##**+++===~~~----:::::...........:
//➜ %%%%%%##**+++===~~~-----::::::......:::
//➜ %%%%%%%##***++====~~~-----::::::::::::-
//➜ %%%%%%%%##***+++====~~~~-------:::::---
//➜ %%%%%%%%%###***+++====~~~~~----------~~
//➜ %%%%%%%%%%%###***++++====~~~~~~~~~~~~~=
//➜ %%%%%%%%%%%%###****++++=============+
//➜ %%%%%%%%%%%%%####****+++++++===+++*
//➜ %%%%%%%%%%%%%%####*******+++***
//➜ %%%%%%%%%%%%%%%%%############
//➜ %%%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%
//➜
echo(
shader((vPos) => {
const theta = uTime / 400;
const sqrt2 = Math.sqrt(2);
const dx = Math.cos(theta) * sqrt2;
const dz = Math.sin(theta) * sqrt2;
const z2 = 1 - vPos.dot(vPos);
const skyColor = new Vector3(0.5, 0.85, 1.5);
const ambient = new Vector3(0.2, 0.1, 0.05);
if (z2 > 0) {
const dir = new Vector3(dx, 1, dz);
const p = new Vector3(vPos.x, vPos.y, Math.sqrt(z2));
const intensity = 0.5 * Math.max(0, p.dot(dir));
const diffuse = skyColor.clone().multiplyScalar(intensity);
const light = diffuse.add(ambient);
return gray2ASCII(new Vector4(light.x, light.y, light.z, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
}),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Shaders
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Computer graphics involves rendering pixels on the screen. Shaders are
* programs that control how pixels are rendered. Here we focus on fragment
* shaders, which are programs that execute once per pixel on the screen,
* determining the color of each pixel.
*
* Since Recho only supports text-based output, our fragment shaders are
* functions that execute once per cell in the output string, determining the
* character displayed in each cell.
*
* Below is our implementation. The `shader` function takes a `callback`
* function and an optional `dimension` argument, returning the output string.
* The `callback` function is evaluated for each cell in the output string,
* receiving the cell's position as a `Vector2` object. The callback's
* return value determines the character displayed in that cell. For each cell,
* the position is normalized to the range of [-1, 1] from left to right, and
* the range of [1, -1] from top to bottom.
*/
function shader(callback, [width, height] = [41, 21]) {
let output = "";
for (let i = 0; i < height; i++) {
const y = map(i, 0, height - 1, 1, -1);
for (let j = 0; j < width; j++) {
const x = map(j, 0, width - 1, -1, 1);
const vPos = new Vector2(x, y);
output += callback(vPos);
}
output += i === height - 1 ? "" : "\n";
}
return output;
}
function map(x, d0, d1, r0, r1) {
return r0 + ((r1 - r0) * (x - d0)) / (d1 - d0);
}
/**
* Since JavaScript doesn't support vector operations, we need to use a
* library to help us. Here we use the vector module in Three.js. We specify
* the version to 0.160.0, because it's the last version that can be imported
* by Recho.
*/
const {Vector2, Vector3, Vector4} = await recho.require("three@0.160.0/build/three.min.js");
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Hello Circle!
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Let's draw a circle to test the shader function. The circle is defined by
* the equation `x^2 + y^2 = 1`. For each cell, we check if the distance from
* the cell to the center of the circle is less than or equal to 1. If it is,
* we draw a `+` character; otherwise, we draw a space character. Here is the
* result:
*/
//➜ +
//➜ +++++++++++++++++
//➜ +++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++++++
//➜ +++++++++++++++++++++++++
//➜ +++++++++++++++++
//➜ +
echo(shader((vPos) => (vPos.length() <= 1 ? "+" : " ")));
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Colors to Characters
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* As mentioned above, actual fragment shaders primarily work with colors.
* Therefore, it's better to focus on colors and convert them to characters
* using simple rules in our text-based shader. A color is typically
* represented by a `Vector4` object, containing the red, green, blue, and
* alpha components. The alpha component is optional and is usually 1 for
* opaque colors.
*
* Let's first implement a rule that converts the grayscale value of colors to
* a sequence of ASCII characters.
*/
function gray2ASCII(color) {
// If the color is transparent, return a space character.
if (color.w !== undefined && color.w === 0) return " ";
const chs = ["@", "%", "#", "*", "+", "=", "~", "-", ":", ".", " "];
const gray = (color.x + color.y + color.z) / 3;
const i = Math.floor(gray * chs.length);
return chs[i];
}
/**
* Then we can use the `gray2ASCII` function as shown below. This example maps
* the x and y components of the position to the red and green components of
* the color respectively, resulting in a gradient.
*/
//➜ ======+++++++++++***********###########%%
//➜ ========+++++++++++***********###########
//➜ ==========+++++++++++***********#########
//➜ ~===========+++++++++++***********#######
//➜ ~~~===========+++++++++++***********#####
//➜ ~~~~~===========+++++++++++***********###
//➜ ~~~~~~~===========+++++++++++***********#
//➜ ~~~~~~~~~===========+++++++++++**********
//➜ ~~~~~~~~~~~===========+++++++++++********
//➜ --~~~~~~~~~~~===========+++++++++++******
//➜ ----~~~~~~~~~~~===========+++++++++++****
//➜ ------~~~~~~~~~~~===========+++++++++++**
//➜ --------~~~~~~~~~~~===========+++++++++++
//➜ ----------~~~~~~~~~~~===========+++++++++
//➜ :-----------~~~~~~~~~~~===========+++++++
//➜ :::-----------~~~~~~~~~~~===========+++++
//➜ :::::-----------~~~~~~~~~~~===========+++
//➜ :::::::-----------~~~~~~~~~~~===========+
//➜ :::::::::-----------~~~~~~~~~~~==========
//➜ :::::::::::-----------~~~~~~~~~~~========
//➜ ..:::::::::::-----------~~~~~~~~~~~======
echo(
shader((vPos) => {
const rgb = new Vector3(vPos.x, vPos.y, 0).multiplyScalar(-0.5).addScalar(0.5);
return gray2ASCII(rgb);
}),
);
/**
* In addition to grayscale, we can also convert the RGB components of colors
* to a sequence of emoji color blocks.
*/
function rgb2emoji(color) {
if (color.w !== undefined && color.w === 0) return " ";
const normalize = (x) => x.map((d) => d / 255);
const emojis = [
{char: "🟥", rgb: normalize([196, 58, 38])},
{char: "🟧", rgb: normalize([240, 144, 54])},
{char: "🟨", rgb: normalize([234, 188, 64])},
{char: "🟩", rgb: normalize([81, 177, 52])},
{char: "🟦", rgb: normalize([40, 92, 233])},
{char: "🟪", rgb: normalize([173, 66, 246])},
{char: "⬛", rgb: normalize([3, 3, 3])},
{char: "⬜", rgb: normalize([217, 217, 217])},
];
let best = emojis[0];
let bestDist = Infinity;
for (const e of emojis) {
const [r, g, b] = e.rgb;
const {x, y, z} = color;
const dist = (x - r) ** 2 + (y - g) ** 2 + (z - b) ** 2;
if (dist < bestDist) {
best = e;
bestDist = dist;
}
}
return best.char;
}
/**
* However, the result is not optimal. Therefore, we'll use the grayscale rule
* for the following examples.
*/
//➜ 🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦⬛⬛⬛⬛⬛⬛⬛⬛
//➜ 🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦🟦🟦🟦🟦⬛⬛⬛⬛
//➜ 🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦🟦🟦🟦🟦🟦🟦🟦🟦⬛
//➜ 🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦
//➜ 🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦
//➜ 🟧🟧🟧🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟥🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦🟦
//➜ 🟧🟧🟧🟧🟧🟧🟥🟥🟥🟥🟥🟥🟥🟩🟩🟩🟩🟦🟦🟦🟦🟦🟦🟦🟦
//➜ 🟧🟧🟧🟧🟧🟧🟧🟧🟧🟥🟥🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟦🟦🟦🟦
//➜ 🟧🟧🟧🟧🟧🟧🟧🟧🟧🟧🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟦
//➜ 🟧🟧🟧🟧🟧🟧🟧🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨🟨🟨🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨🟨🟨⬜⬜⬜🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
//➜ 🟨🟨🟨🟨🟨🟨⬜⬜⬜⬜⬜🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩🟩
echo(
shader(
(vPos) => {
const rgb = new Vector3(vPos.x, vPos.y, 0).multiplyScalar(-0.5).addScalar(0.5);
return rgb2emoji(rgb);
},
[25, 17],
),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* First Sphere
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Now let's draw a sphere. The sphere is defined by the equation `x^2 + y^2 +
* z^2 = 1`. First, for each vPos (x, y), we compute the z component using
* `1 - x^2 - y^2`, which is equivalent to `1 - vPos.dot(vPos)`. If z is
* valid (z > 0), we compute the color of that cell; otherwise, we set the
* color to transparent.
*
* We assign the z component to the red and green components of the color.
* The larger the z value (closer to the center), the brighter the color
* appears. This simulates a beam of light shining perpendicularly onto the
* screen from outside.
*/
//➜
//➜ %%###*******###%%
//➜ %##****+++++++++****##%
//➜ %##**+++++=========+++++**##%
//➜ ##**+++=================+++**##
//➜ %#**+++=====~~~~~~~~~~~=====+++**#%
//➜ %#**++====~~~~~~~~~~~~~~~~~====++**#%
//➜ @#**++====~~~~~~~~~~~~~~~~~~~====++**#@
//➜ %#*++====~~~~~~---------~~~~~~====++*#%
//➜ #**++===~~~~~~-----------~~~~~~===++**#
//➜ #**++===~~~~~~-----------~~~~~~===++**#
//➜ #**++===~~~~~~-----------~~~~~~===++**#
//➜ %#*++====~~~~~~---------~~~~~~====++*#%
//➜ @#**++====~~~~~~~~~~~~~~~~~~~====++**#@
//➜ %#**++====~~~~~~~~~~~~~~~~~====++**#%
//➜ %#**+++=====~~~~~~~~~~~=====+++**#%
//➜ ##**+++=================+++**##
//➜ %##**+++++=========+++++**##%
//➜ %##****+++++++++****##%
//➜ %%###*******###%%
//➜
echo(
shader((vPos) => {
const z2 = 1 - vPos.dot(vPos);
if (z2 > 0) {
const z = Math.sqrt(z2);
return gray2ASCII(new Vector4(z, 0, z, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
}),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Diffuse Reflection Model
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Next, we use the diffuse reflection model to make the sphere more realistic.
* Given a directional light source, the intensity of light on a surface is
* proportional to the cosine of the angle between the light direction and the
* surface normal. For a sphere, the surface normal at point (x, y, z) is the
* normalized vector `(x, y, z)`.
*
* Here we define a light direction `dir` (1, 1, 1). For each point `p`, we use
* the dot product between `p` and `dir` to compute the light intensity.
*/
//➜
//➜ *+===~~----::::::
//➜ #*++==~~~----:::::...::
//➜ @%#**++==~~~---:::::........:
//➜ @%##**++==~~~----::::.........:
//➜ @@%%##**++===~~~---:::::.........::
//➜ @@@@%##**+++==~~~~----:::::........::
//➜ @@@@@%%##**+++==~~~~----:::::::....:::-
//➜ @@@@@%%###**+++===~~~-----::::::::::::-
//➜ @@@@@@%%###**+++===~~~~------::::::::--
//➜ @@@@@@@%%###***+++===~~~~~------------~
//➜ @@@@@@@@@%%##***++++====~~~~~~------~~~
//➜ @@@@@@@@@@%%###***++++=====~~~~~~~~~~==
//➜ @@@@@@@@@@@@%%###****+++++============+
//➜ @@@@@@@@@@@@@%%%###****+++++++++++++*
//➜ @@@@@@@@@@@@@@%%%#####************#
//➜ @@@@@@@@@@@@@@@%%%%############
//➜ @@@@@@@@@@@@@@@@@@%%%%%%%%%%@
//➜ @@@@@@@@@@@@@@@@@@@@@@@
//➜ @@@@@@@@@@@@@@@@@
//➜
echo(
shader((vPos) => {
const z2 = 1 - vPos.dot(vPos);
if (z2 > 0) {
const dir = new Vector3(1, 1, 1);
const p = new Vector3(vPos.x, vPos.y, Math.sqrt(z2));
const intensity = 0.5 * Math.max(0, p.dot(dir));
return gray2ASCII(new Vector4(intensity, intensity, intensity, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
}),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Ambient Light
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* To make the sphere appear smoother, we can add ambient lighting to the
* sphere. Ambient light is constant lighting that is not affected by the
* direction of the light source.
*
* Here we simply add the ambient light to the diffuse light to obtain the
* final lighting. The sphere appears brighter, and the transitions between
* layers are more natural.
*/
//➜
//➜ +=~~~---::::....:
//➜ *+==~~---::::..........
//➜ #**++==~~---::::..... ..
//➜ %#*++===~~---::::..... .
//➜ %%##*+++==~~~---::::...... ..
//➜ %%%##**++===~~----::::....... ..:
//➜ %%%%##**+++==~~~~---:::::.............:
//➜ %%%%%##**+++===~~~----:::::...........:
//➜ %%%%%%##**+++===~~~-----::::::......:::
//➜ %%%%%%%##***++====~~~-----::::::::::::-
//➜ %%%%%%%%##***+++====~~~~-------:::::---
//➜ %%%%%%%%%###***+++====~~~~~----------~~
//➜ %%%%%%%%%%%###***++++====~~~~~~~~~~~~~=
//➜ %%%%%%%%%%%%###****++++=============+
//➜ %%%%%%%%%%%%%####****+++++++===+++*
//➜ %%%%%%%%%%%%%%####*******+++***
//➜ %%%%%%%%%%%%%%%%%############
//➜ %%%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%
//➜
echo(
shader((vPos) => {
const z2 = 1 - vPos.dot(vPos);
const skyColor = new Vector3(0.5, 0.85, 1.5);
const ambient = new Vector3(0.2, 0.1, 0.05);
if (z2 > 0) {
const dir = new Vector3(1, 1, 1);
const p = new Vector3(vPos.x, vPos.y, Math.sqrt(z2));
const intensity = 0.5 * Math.max(0, p.dot(dir));
const diffuse = skyColor.clone().multiplyScalar(intensity);
const light = diffuse.add(ambient);
return gray2ASCII(new Vector4(light.x, light.y, light.z, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
}),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Rotating Sphere
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Next, we make the sphere rotate around the y-axis. We can use the time
* variable to compute the direction of the light. The key is to change the `x`
* and `z` components of the light direction.
*
* We define a time variable `uTime` using `recho.now()`, which is a generator
* that yields the current time continuously. Every time the time variable
* changes, the referencing block (shader) will be re-evaluated, resulting in
* smooth animations.
*/
const uTime = recho.now();
//➜
//➜ ####*****+++==~~-
//➜ %%%%%%%%%####***++==~~-
//➜ %%%%%%%%%%%%%%%%###**+++==~-:
//➜ %%%%%%%%%%%%%%%%%%%%##***++==~-
//➜ %%%%%%%%%%%%%%%%%%%%%%%%##***++=~~:
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%##**++==~-
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%##**+==~-
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%##**++=~
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%##**+==
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%#**+=
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%##**+
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%##*+
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%#*+
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%#*
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%#
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%
//➜
echo(
shader((vPos) => {
const theta = uTime / 400;
const sqrt2 = Math.sqrt(2);
const dx = Math.cos(theta) * sqrt2;
const dz = Math.sin(theta) * sqrt2;
const z2 = 1 - vPos.dot(vPos);
const skyColor = new Vector3(0.5, 0.85, 1.5);
const ambient = new Vector3(0.2, 0.1, 0.05);
if (z2 > 0) {
const dir = new Vector3(dx, 1, dz);
const p = new Vector3(vPos.x, vPos.y, Math.sqrt(z2));
const intensity = 0.5 * Math.max(0, p.dot(dir));
const diffuse = skyColor.clone().multiplyScalar(intensity);
const light = diffuse.add(ambient);
return gray2ASCII(new Vector4(light.x, light.y, light.z, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
}),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Moving Sphere
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Let's not only rotate the sphere, but also move it. This can be achieved by
* updating the position and radius of the sphere.
*/
//➜
//➜
//➜
//➜
//➜
//➜
//➜
//➜
//➜
//➜
//➜
//➜ #***
//➜ %%%%%%%####***
//➜ %%%%%%%%%%%%%###***
//➜ %%%%%%%%%%%%%%%%###**+
//➜ %%%%%%%%%%%%%%%%%%%###**
//➜ %%%%%%%%%%%%%%%%%%%%%%##**
//➜ %%%%%%%%%%%%%%%%%%%%%%%##*
//➜ %%%%%%%%%%%%%%%%%%%%%%%%#*
//➜ %%%%%%%%%%%%%%%%%%%%%%%%#
//➜ %%%%%%%%%%%%%%%%%%%%%%%#
//➜ %%%%%%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%%%%%%%
//➜ %%%%%%%%%%%%
//➜
//➜
//➜
//➜
//➜
//➜
//➜
echo(
shader(
(vPos) => {
const now = uTime / 2000;
const theta = uTime / 400;
const sqrt2 = Math.sqrt(2);
const dx = Math.cos(theta) * sqrt2;
const dz = Math.sin(theta) * sqrt2;
const r = 0.3 + 0.2 * Math.sin(4 * now);
const x = vPos.x + 0.5 * Math.sin(5 * now);
const y = vPos.y + 0.5 * Math.sin(7 * now);
const z2 = r * r - (x * x + y * y);
const skyColor = new Vector3(0.5, 0.85, 1.5);
const ambient = new Vector3(0.2, 0.1, 0.05);
if (z2 > 0) {
const dir = new Vector3(dx, 1, dz);
const p = new Vector3(x, y, Math.sqrt(z2));
const intensity = 0.5 * Math.max(0, p.dot(dir));
const diffuse = skyColor.clone().multiplyScalar(intensity);
const light = diffuse.add(ambient);
return gray2ASCII(new Vector4(light.x, light.y, light.z, 1));
}
return gray2ASCII(new Vector4(0, 0, 0, 0));
},
[61, 31],
),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* More Spheres with more Lights
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* Our final example is more complex, featuring multiple spheres and multiple
* lights. However, the concept remains the same as the previous examples.
* The only difference is that for each cell, we need to compute the color for
* each sphere, then select the one closest to the screen as the final color.
*/
//➜
//➜ ####***++
//➜ **###### ########***
//➜ ########### ############
//➜ ############# ###########
//➜ ############# #########
//➜ ############# #
//➜ #########
//➜
//➜ ####****+
//➜ ########***
//➜ ###########*
//➜ ###########
//➜ #########
//➜ ###
//➜ %%*****+++=
//➜ %%********+++
//➜ %%%***********+
//➜ %%%***********
//➜ %%%*********
//➜ %%%*** ##***++
//➜ %%###****++
//➜ %%#######****
//➜ %%##########**
//➜ *#****+++ %###########
//➜ ######****+ %%#######
//➜ #########***
//➜ ###########
//➜ ##########
//➜ #####
//➜
echo(
shader(
(vPos) => {
const scale = 5;
const now = uTime / 1000;
const ambient = new Vector3(0.2, 0.1, 0.05);
let fragColor = new Vector4(0, 0, 0, 0);
let zMax = -1000;
const L1 = new Vector3(Math.sin(now * 2), 1, 0).normalize();
const L2 = new Vector3(-1, -0.1, 0).normalize();
for (let i = 0; i < 10; i++) {
const x = scale * vPos.x + 4 * Math.sin(11.8 * i + 100.3 + 0.3 * now);
const y = scale * vPos.y + 4 * Math.sin(10.3 * i + 200.6 + 0.3 * now);
const z = scale * vPos.y + 4 * Math.cos(10.3 * i + 200.6 + 0.3 * now);
const r = 1 * 1 - (x * x + y * y);
const z1 = z + r / (scale * scale);
if (r > 0 && z1 > zMax) {
zMax = z1;
const p = new Vector3(x, y, Math.sqrt(r));
let D1 = p.clone().dot(L1);
let D2 = p.clone().dot(L2);
D1 = 0.4 * Math.max(0, D1 * Math.abs(D1));
D2 = 0.4 * Math.max(0, D1 * Math.abs(D2));
const d1 = new Vector3(0.2, 0.5, 1).multiplyScalar(D1);
const d2 = new Vector3(0.2, 0.5, 1).multiplyScalar(D2);
const diffuse = d1.add(d2);
const color = new Vector3(0.5 + 0.5 * Math.sin(i), 0.5 + 0.5 * Math.sin(4 * i), 0.5 + 0.5 * Math.sin(5 * i));
const light = color.multiply(diffuse.add(ambient));
return gray2ASCII(new Vector4(Math.sqrt(light.x), Math.sqrt(light.y), Math.sqrt(light.z), 1));
}
}
return gray2ASCII(fragColor);
},
[61, 31],
),
);
/**
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* Summary
* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
*
* In this tutorial, we have learned how to use shaders to create basic
* computer graphics effects. We have learned how to use the diffuse reflection
* model to compute lighting, how to use ambient lighting to make the sphere
* appear smoother, how to use the time variable to create animations, and how
* to use multiple spheres and lights to create more complex effects.
*
* I hope you have enjoyed this tutorial. If you have any questions, please
* feel free to comment on https://github.com/recho-dev/notebook/issues/98.
*/