You were probably getting sick of me saying stuff like, "We'll get to that when we talk about buffers". Well, now's the time to finally talk about buffers, but first...
## What is a buffer?
A buffer is a blob of data on the GPU. A buffer is guaranteed to be contiguous, meaning that all the data is stored sequentially in memory. Buffers are generally used to store simple things like structs or arrays, but they can store more complex stuff such as graph structures like trees (provided all the nodes are stored together and don't reference anything outside the buffer). We are going to use buffers a lot, so let's get started with two of the most important ones: the vertex buffer and the index buffer.
## The vertex buffer
Previously, we've stored vertex data directly in the vertex shader. While that worked fine to get our bootstraps on, it simply won't do for the long term. The types of objects we need to draw will vary in size, and recompiling the shader whenever we need to update the model would massively slow down our program. Instead, we are going to use buffers to store the vertex data we want to draw. Before we do that, though, we need to describe what a vertex looks like. We'll do this by creating a new struct.
```rust
@ -435,7 +438,9 @@ If you use a color picker on the magenta pentagon, you'll get a hex value of #BC
Most monitors use a color space known as sRGB. Our surface is (most likely depending on what is returned from `surface.get_preferred_format()`) using an sRGB texture format. The sRGB format stores colors according to their relative brightness instead of their actual brightness. The reason for this is that our eyes don't perceive light linearly. We notice more differences in darker colors than in lighter colors.
You get the correct color using the following formula: `srgb_color = ((rgb_color / 255 + 0.055) / 1.055) ^ 2.4`. Doing this with an RGB value of (188, 0, 188) will give us (0.5028864580325687, 0.0, 0.5028864580325687). A little off from our (0.5, 0.0, 0.5). Instead of doing a manual color conversion, you'll likely save a lot of time by using textures instead, as they are stored as sRGB by default, so they don't suffer from the same color inaccuracies that vertex colors do. We'll cover textures in the next lesson.
Most software that uses colors stores them in sRGB format (or a similar proprietary one). Wgpu expects values in linear color space, so we have to convert the values.
You get the correct color using the following formula: `rgb_color = ((srgb_color / 255 + 0.055) / 1.055) ^ 2.4`. Doing this with an sRGB value of (188, 0, 188) will give us (0.5028864580325687, 0.0, 0.5028864580325687). A little off from our (0.5, 0.0, 0.5). Instead of doing a manual color conversion, you'll likely save a lot of time by using textures instead, as if they are store in an sRGB texture, the conversion to linear will happen automatically. We'll cover textures in the next lesson.
## Challenge
Create a more complex shape than the one we made (aka. more than three triangles) using a vertex buffer and an index buffer. Toggle between the two with the space key.
@ -429,9 +429,13 @@ We get the following from this calculation.
## Srgb and normal textures
We've been using `Rgba8UnormSrgb` for all our textures. The `Srgb` bit specifies that we will be using [standard RGB (red, green, blue) color space](https://en.wikipedia.org/wiki/SRGB). This is also known as linear color space. Linear color space has less color density. Even so, it is often used for diffuse textures, as they are typically made in `Srgb` color space.
We've been using `Rgba8UnormSrgb` for all our textures. Srgb is a non-linear color space. It is ideal for monitors because human color perception isn't linear either and Srgb was designed to match the quirkiness of our human color perception.
Normal textures aren't made with `Srgb`. Using `Rgba8UnormSrgb` can change how the GPU samples the texture. This can make the resulting simulation [less accurate](https://medium.com/@bgolus/generating-perfect-normal-maps-for-unity-f929e673fc57#b86c). We can avoid these issues by using `Rgba8Unorm` when we create the texture. Let's add an `is_normal_map` method to our `Texture` struct.
But Srgb is an inappropriate color space for data that must be operated on mathematically. Such data should be in a linear (not gamma-corrected) color space. When a GPU samples a texture with Srgb in the name, it converts the data from non-linear gamma-corrected Srgb to a linear non-gamma-corrected color space first so that you can do math on it (and it does the opposite conversion if you write back to a Srgb texture).
Normal maps are already stored in a linear format. So we should be specifying the linear space for the texture so it doesn't do an inappropriate conversion when we read from it.
We need to specify `Rgba8Unorm` when we create the texture. Let's add an `is_normal_map` method to our Texture struct.
Benjamin Hansen
1 month ago