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Game Systems Tech Details

Clouds

Overview

Clouds use a noise based fast-cloud approach:

  • Flat 2D cloud pieces (no volumetric mesh).
  • Fixed cloud height (layer_y, default 108.5f, the .5 is to prevent z-figthing for now).
  • Constant westward drift (speed_x < 0).

The system is lightweight and generated once at startup.

Data Model

Cloud runtime data lives in Clouds (src/gfx/clouds.h):

  • scroll_x: horizontal movement offset for cloud drift.
  • speed_x: horizontal drift speed (-0.9f default, westward).
  • cell_size: world size of one cloud cell (8.0f default).
  • layer_y: fixed Y level for cloud layer (108.0f default).
  • radius_cells: draw radius around camera in cell units (26 default).
  • noise_size: generated source image size (256 default).
  • block_px: pixels per cloud cell in source map (8 default).
  • grid_size: derived map side length in cells (noise_size / block_px).
  • cloud_opacity: final alpha multiplier for cloud tiles (0.7f default).
  • cell_map: binary occupancy map (0 = empty, 1 = cloud).

Generation (Init)

Clouds_Init() generates cloud layout once:

  1. GenImagePerlinNoise() creates a grayscale noise image.
  2. Image is divided into block_px x block_px blocks.
  3. Each block average brightness is thresholded (avg >= 142) into one binary cloud cell.
  4. Result is stored in cell_map and reused every frame.

This gives a procedural clouds.png-style repeating bitmap map.

Update

Clouds_Update() only advances drift:

  • scroll_x += speed_x * dt

No per-cell simulation or regeneration runs every frame.

Rendering

Clouds_Draw():

  1. Converts camera position into cloud-cell coordinates.
  2. Iterates a bounded square (radius_cells) around the camera.
  3. Wraps world cell coordinates into cell_map indices (infinite tiling).
  4. Draws one flat quad for every occupied cell using DrawTriangle3D.

Render state:

  • Depth test and depth writes are disabled during cloud draw.
  • Backface culling is disabled so tiles are visible from below.
  • State is restored after cloud pass.

Coloring:

  • Brightness tint is derived from ambient (220 + 35 * ambient_multiplier).
  • Alpha comes from cloud_opacity (cloud_opacity * 255).

Cloud pass order is sky-first in game_draw_world_pass():

  • Clouds_Draw(...)
  • World_Draw(...)

So terrain draws over clouds naturally.

Tuning Knobs

Primary parameters in Clouds_Init() (src/gfx/clouds.c):

  • cell_size: larger = chunkier cloud pieces.
  • radius_cells: larger = farther cloud horizon, more draw cost.
  • layer_y: cloud layer altitude.
  • speed_x: drift speed and direction.
  • noise_size: map repeat period (world tiling frequency).
  • block_px: cell granularity from source image (higher = bigger blob features).
  • cloud_opacity: overall transparency of clouds.
  • threshold constant (avg >= 142): controls cloud coverage density.