Find a better system to handle empty texture properties (bindless textures?)

[adriengivry]

Problem this feature should fix

Right now when a texture isn't provided on a material, a default texture is attached instead.

• 2D texture: white pixel (255, 255, 255, 255)
• Cubemap texture: black pixel (0, 0, 0, 0) for each face

Expected solution

We should implement a system to provide more options to shaders to choose what the default "no-texture set" behaviour should be.

We could either:

• Not provide any texture, and let the shader check if a texture is passed using textureQueryLod(). If textureQueryLod() returns 0, no texture is bound, so a backup color/behaviour can be selected.
• Let shader uniforms specify what type of default texture they require (similar to unity, were properties can define the color of the default texture): _MainTex("Texture",2D)="white"{}.

It could look like:

uniform sampler2D albedo; [default = "white"]

I'm leaning toward using textureQueryLod(), since the overhead should be minimal, and would give more control to the user. With the other method, we would need to define a fixed set of preset textures, while using textureQueryLod will let the user choose anything, or even branch out and skip a code-block completely. This would also reduce the amount of textures binds, which could potentially improve performance.

Edit: I think we should look into bindless textures!

[adriengivry]

One way to check if a texture is unbound or 1x1:

// Check if the texture is bound by comparing its size to default texture sizes.
// If not texture is bound, it's expected to have a size of 1x1 or less.
bool IsDefaultOrUnboundTexture(sampler2D tex)
{
    const ivec2 texSize = textureSize(tex, 0);
    return texSize.x <= 1 && texSize.y <= 1;
}

textureQueryLod doesn't seem to work well.

Another approach would be to use bindless textures