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1. UV Coordinates

Your Understanding: "In 2D, UV coordinates are just the vertex location of a tile in the tilemap?"

Correction and Explanation:

  • UV Coordinates are not the vertex locations of a tile in the tilemap. Instead, they are **texture coordinates ** used to map a 2D image (texture) onto the surface of a 3D or 2D geometry (mesh).
  • Think of UV coordinates as a way to tell the GPU which part of a texture image should be applied to a particular vertex or fragment (pixel) of your mesh.

In the Context of Your Game:

  • UV Coordinates range from (0, 0) to (1, 1), representing the bottom-left and top-right corners of the texture image, respectively.
  • Each vertex of a tile's mesh has associated UV coordinates that map to positions on the texture atlas (an image containing all your tile textures).
  • When rendering, the GPU uses these UV coordinates to sample the correct portion of the texture atlas for each tile.

In Your Shader Code:

  • In the vertex shader, UV coordinates are calculated for each vertex based on the tile's texture index and any flip or rotation flags.
  • These UV coordinates are passed to the fragment shader, which uses them to sample the texture and obtain the color for each pixel.
  • In your fragment shader, you're also using the UV coordinates, along with the tile's position, to compute the world position of each fragment for the fog effect.

2. Mesh

Your Understanding: "In 2D and bevy_ecs_tilemap, it's just the Tilemap as set by being Square type?"

Explanation:

  • A mesh is a collection of vertices, edges, and faces that define the shape of a 3D or 2D object.
  • In 2D games, meshes are flat, but they still consist of vertices and faces (typically triangles or quads).

In the Context of Your Game and bevy_ecs_tilemap:

  • Each tile in your tilemap is represented by a quad (a square made up of two triangles), which is a simple mesh.
  • The TilemapType::Square indicates that the tiles are square-shaped, and the mesh generation logic will create quads for each tile.
  • bevy_ecs_tilemap groups tiles into chunks for efficient rendering. Each chunk has its own mesh containing the geometry (vertices, indices, UVs) for all tiles in that chunk.

Key Points:

  • The mesh represents the geometry that will be rendered on the screen.
  • The vertex shader processes the mesh's vertices, transforming their positions and passing data to the fragment shader.

3. Vertex Shader

Your Understanding: "The part of the rendering that just lays down the tiles into their designated indices by taking from the texture atlas and placing down on the tilemap? Nothing special."

Correction and Explanation:

  • The vertex shader processes each vertex of the mesh. Its primary roles are:
    • Transforming Vertex Positions: Converts vertex positions from model space to world space, and then to clip space (so they can be rendered correctly on the screen).
    • Passing Data to the Fragment Shader: Calculates and passes per-vertex data (like UV coordinates, colors, normals) to the fragment shader.
  • The vertex shader does not "lay down" tiles by taking from the texture atlas—that's handled by the fragment shader through texture sampling.

In the Context of Your Game:

  • The vertex shader provided by bevy_ecs_tilemap:
    • Transforms Positions: Applies necessary transformations so that each tile appears in the correct position on the screen.
    • Handles Animations: Calculates the correct frame for animated tiles by adjusting UV coordinates based on time.
    • Calculates UVs: Determines the correct UV coordinates for each vertex, taking into account texture atlases, tile flipping, and rotation.

Key Points:

  • The vertex shader prepares data for the fragment shader but doesn't perform texture sampling or per-pixel calculations.
  • It's essential for positioning tiles correctly and ensuring that the right texture coordinates are used.

4. Fragment Shader

Your Understanding: "My custom one with the introduction of the time uniform allows for animation based on per-pixel processing of the world coordinates?"

Confirmation and Explanation:

  • Correct! The fragment shader computes the final color of each pixel (fragment) that will be rendered on the screen.
  • It runs for every pixel covered by a primitive (e.g., a triangle) and determines what color that pixel should be.

In the Context of Your Game:

  • Your custom fragment shader:
    • Uses Uniforms: Receives time, density, fog_color, and wind_dir from the FogMaterial uniform.
    • Per-Pixel Processing: Calculates the fog effect for each pixel based on its world position and the current time.
    • Procedural Noise: Utilizes noise functions (like value noise and fractal Brownian motion) to create dynamic, natural-looking fog patterns.
    • Animation: The time uniform changes every frame (updated in your system), causing the fog pattern to move and evolve over time.
    • World Coordinates: Computes the world position of each fragment to ensure the fog pattern aligns correctly across the tilemap.

Key Points:

  • The fragment shader is where you implement per-pixel effects like your animated fog.
  • By updating the time uniform, you animate the fog without needing to modify the vertex shader.

5. World Coordinates

Your Understanding: "The literal x,y pixels that bounds the tilemap."

Correction and Explanation:

  • World Coordinates are positions in the game world, in world space. They represent where objects are located within the game's coordinate system.
  • They are not pixels; rather, they are units in your game's coordinate system (e.g., meters, tiles).

In the Context of Your Game:

  • In your fragment shader, you compute the world position of each fragment (pixel) by:
    • Calculating the tile's global position within the tilemap.
    • Adding the local position within the tile (using UV coordinates scaled by tile size).
  • This world position is crucial for ensuring that the fog pattern moves consistently across the entire tilemap, regardless of the camera's position.

Key Points:

  • World coordinates allow you to apply effects (like fog) that are consistent across the game world.
  • They are essential for procedural effects that depend on position, ensuring continuity across tiles.

6. Tile Coordinates

Your Understanding: "The x,y tiles that make up the tilemap (in shader context this is just the UV coordinates, right?)"

Correction and Explanation:

  • Tile Coordinates are the positions of tiles within the tilemap grid, typically represented by integer indices ( e.g., (5, 10) for the tile at column 5, row 10).
  • In the shader context, tile coordinates are not the same as UV coordinates.
    • Tile Coordinates: Grid positions of tiles within the tilemap.
    • UV Coordinates: Texture coordinates used for mapping textures onto geometry, ranging from (0, 0) to (1, 1).

In the Context of Your Game:

  • You use the tile's position (TilePos) to determine its location in the tilemap.
  • In the shader, in.storage_position contains the tile coordinates.
  • These coordinates are used to calculate the world position of each fragment for the fog effect.

Key Points:

  • Tile coordinates help you determine where each tile is in the game world.
  • They are used in the shader to align effects like fog with the tilemap grid.

7. Clip Space

Your Understanding: "The normalized projection of the whole tilemap (or in other words all the tiles/UV coordinates) onto the screen/window."

Correction and Explanation:

  • Clip Space is a coordinate space used during the rendering pipeline, specifically after the projection transformation but before perspective division.
  • It's not the normalized projection; that comes after clip space.
  • Clip Space coordinates are in homogeneous coordinates (x, y, z, w).

Rendering Pipeline Context:

  1. Model Space: The object's local coordinate system.
  2. World Space: The coordinate system of the game world.
  3. View Space: Coordinates relative to the camera's position and orientation.
  4. Clip Space: Result of applying the projection matrix to view space coordinates.
  5. Normalized Device Coordinates (NDC): Obtained by dividing clip space coordinates by w (perspective division), resulting in coordinates ranging from -1 to 1.
  6. Screen Space: NDC transformed to window coordinates (pixels).

In the Context of Your Game:

  • In the vertex shader, you transform positions to clip space using the view-projection matrix.
  • Clip space is used by the GPU to determine which vertices are within the view frustum (the visible area).
  • It's an intermediate space that the GPU uses before rasterizing the primitives and running the fragment shader.

Key Points:

  • Clip space is essential for the GPU's rendering pipeline but isn't directly manipulated in most shaders.
  • Understanding clip space helps in debugging rendering issues like objects not appearing on the screen.

8. View

Your Understanding: "Another space that is just a subset of the clip space based on how the camera is configured."

Correction and Explanation:

  • View Space (also known as Camera Space or Eye Space) is a coordinate system where positions are relative to the camera's position and orientation.
  • It is obtained by transforming world space coordinates by the view matrix (which represents the camera's transformation).
  • View Space is not a subset of clip space; it is an earlier step in the transformation pipeline.

Rendering Pipeline Context:

  • World Space → View Space: Apply the view (camera) transformation.
  • View Space → Clip Space: Apply the projection transformation.

In the Context of Your Game:

  • The view matrix represents the camera's position and orientation in the world.
  • The vertex shader uses the view matrix to transform world positions to view space.
  • This ensures that objects are rendered from the camera's perspective.

Key Points:

  • View space is crucial for simulating a camera's point of view.
  • It's an intermediate step before applying the projection matrix to get to clip space.

Additional Context: The Rendering Pipeline and Coordinate Spaces

Understanding the transformation pipeline is key to grasping how vertex positions are processed and how shaders work together.

1. Model Space

  • Coordinates relative to an object's local origin.
  • For tiles, this might be the local coordinates of the quad representing the tile.

2. World Space

  • Positions in the game world.
  • Obtained by applying the model matrix (object's transformation) to model space coordinates.
  • In tilemaps, tiles are positioned in world space based on their tile coordinates and tile size.

3. View Space

  • Coordinates relative to the camera's position and orientation.
  • Obtained by applying the view matrix to world space coordinates.

4. Clip Space

  • Result of applying the projection matrix to view space coordinates.
  • Used for clipping primitives outside the view frustum.

5. Normalized Device Coordinates (NDC)

  • Obtained by performing perspective division (dividing clip space coordinates by w).
  • Coordinates range from -1 to 1 in all three axes.

6. Screen Space

  • NDC transformed to window coordinates, typically in pixels.
  • This is where the rasterizer determines which pixels correspond to each primitive.

Bringing It All Together in Your Game

  • Vertex Shader:

    • Transforms each vertex from model space to world space, then to view space, and finally to clip space.
    • Calculates UV coordinates for texture sampling.
    • Passes per-vertex data (like UVs and positions) to the fragment shader.

  • Fragment Shader:

    • Runs for each pixel covered by a primitive.
    • Uses interpolated data from the vertex shader (e.g., UVs, colors).
    • Samples the texture using UV coordinates.
    • Computes the world position of each fragment for procedural effects.
    • Applies the fog effect using per-pixel calculations based on world position and time.

  • Tile Coordinates vs. UV Coordinates:

    • Tile Coordinates: Indices in the tilemap grid (e.g., tile at position (x, y)).
    • UV Coordinates: Used to map textures onto the mesh, ranging from (0, 0) to (1, 1) for the full texture.

  • World Coordinates in Fog Effect:

    • Essential for ensuring the fog pattern is continuous and consistent across tiles.
    • By computing the world position of each fragment, you avoid seams or discontinuities in the fog effect.

Conclusion

Understanding these terms and how they interrelate in the rendering pipeline is crucial for effective shader programming and game development. In your game:

  • UV Coordinates map textures onto your tiles.
  • Meshes represent the geometry of your tiles.
  • The vertex shader transforms vertex positions and passes data to the fragment shader.
  • Your custom fragment shader creates the fog effect by processing each pixel.
  • World Coordinates are used to ensure the fog moves consistently over your tilemap.
  • Tile Coordinates help determine where each tile is in the grid.
  • Clip Space and View Space are part of the transformation pipeline that positions your tiles correctly on the screen.