WebOcean/src/OceanLOD.ts

import { Grid } from './Grid';
import { vec3 } from 'gl-matrix';

/** Manages multiple ocean grid patches with LOD based on camera distance and view cone */
export class OceanLOD {
    private grids: Array<{ 
        grid: Grid; 
        centerX: number; 
        centerY: number;
        size: number;
        lodLevel: number;
        visible: boolean;
    }> = [];
    
    private readonly LOD_LEVELS = [
        { distance: 3.0, gridSize: 256 },   // Very close - ultra detail
        { distance: 8.0, gridSize: 128 },   // Close - high detail
        { distance: 20.0, gridSize: 64 },   // Medium distance
        { distance: 40.0, gridSize: 16 },   // Far - low detail
        { distance: 80.0, gridSize: 8 },    // Very far - minimal
        { distance: Infinity, gridSize: 4 },// Horizon - lowest (will be stretched anyway)
    ];
    
    private readonly PATCH_SIZE = 10.0; // Larger patches = fewer needed
    private readonly PATCHES_PER_SIDE = 21; // 21x21 = 441 patches (covers ~200 units)
    private readonly VIEW_CONE_COS = Math.cos(Math.PI * 0.45); // ~81 degree half-angle (wider than typical FOV)
    
    // Track the grid origin to re-center when camera moves
    private gridOriginX: number = 0;
    private gridOriginY: number = 0;
    
    constructor() {
        this.createGridPatches();
    }
    
    private createGridPatches(): void {
        const halfPatches = Math.floor(this.PATCHES_PER_SIDE / 2);
        
        for (let y = -halfPatches; y <= halfPatches; y++) {
            for (let x = -halfPatches; x <= halfPatches; x++) {
                const centerX = x * this.PATCH_SIZE + this.gridOriginX;
                const centerY = y * this.PATCH_SIZE + this.gridOriginY;
                
                // Start with lowest detail - will be updated based on camera
                const grid = new Grid(
                    this.LOD_LEVELS[5].gridSize,
                    centerX,
                    centerY,
                    this.PATCH_SIZE
                );
                
                this.grids.push({
                    grid,
                    centerX,
                    centerY,
                    size: this.PATCH_SIZE,
                    lodLevel: 5,
                    visible: true
                });
            }
        }
    }
    
    /** Re-center the grid around a new origin */
    private recenterGrid(gl: WebGL2RenderingContext, newOriginX: number, newOriginY: number): void {
        this.gridOriginX = newOriginX;
        this.gridOriginY = newOriginY;
        
        const halfPatches = Math.floor(this.PATCHES_PER_SIDE / 2);
        let i = 0;
        
        for (let y = -halfPatches; y <= halfPatches; y++) {
            for (let x = -halfPatches; x <= halfPatches; x++) {
                const patch = this.grids[i];
                const newCenterX = x * this.PATCH_SIZE + this.gridOriginX;
                const newCenterY = y * this.PATCH_SIZE + this.gridOriginY;
                
                // Only update if patch position changed
                if (patch.centerX !== newCenterX || patch.centerY !== newCenterY) {
                    patch.centerX = newCenterX;
                    patch.centerY = newCenterY;
                    // Force LOD recalculation
                    patch.lodLevel = -1;
                }
                i++;
            }
        }
    }
    
    /** Update LOD based on camera position and view direction */
    updateLOD(gl: WebGL2RenderingContext, cameraPos: vec3, cameraTarget: vec3): void {
        // Calculate view direction (normalized)
        const viewDir = vec3.create();
        vec3.subtract(viewDir, cameraTarget, cameraPos);
        vec3.normalize(viewDir, viewDir);
        
        // Check if we need to recenter the grid (camera moved more than one patch size from origin)
        const cameraGridX = Math.floor(cameraPos[0] / this.PATCH_SIZE) * this.PATCH_SIZE;
        const cameraGridY = Math.floor(cameraPos[1] / this.PATCH_SIZE) * this.PATCH_SIZE;
        
        if (cameraGridX !== this.gridOriginX || cameraGridY !== this.gridOriginY) {
            this.recenterGrid(gl, cameraGridX, cameraGridY);
        }
        
        for (const patch of this.grids) {
            // Calculate vector from camera to patch center (on XY plane, Z=0 for ocean surface)
            const toPatch = vec3.fromValues(
                patch.centerX - cameraPos[0],
                patch.centerY - cameraPos[1],
                0 - cameraPos[2]  // Ocean is at Z=0
            );
            const distance = vec3.length(toPatch);
            
            // Normalize direction to patch
            const toPatchDir = vec3.create();
            vec3.normalize(toPatchDir, toPatch);
            
            // Calculate dot product with view direction (how aligned is patch with where we're looking)
            const dotProduct = vec3.dot(viewDir, toPatchDir);
            
            // Determine if patch is in front of camera and within view cone
            const isInFront = dotProduct > -0.3; // Slightly behind is ok for edge cases
            const isInViewCone = dotProduct > this.VIEW_CONE_COS;
            
            // Frustum culling - don't draw patches behind camera
            patch.visible = isInFront;
            
            // Calculate LOD level
            let newLodLevel = 5; // Default to lowest detail
            
            if (!isInFront) {
                // Behind camera - skip (will not be drawn)
                newLodLevel = 5;
            } else if (isInViewCone) {
                // In view cone - use distance-based LOD
                for (let i = 0; i < this.LOD_LEVELS.length; i++) {
                    if (distance < this.LOD_LEVELS[i].distance) {
                        newLodLevel = i;
                        break;
                    }
                }
            } else {
                // In front but outside view cone - reduce detail by 1-2 levels
                for (let i = 0; i < this.LOD_LEVELS.length; i++) {
                    if (distance < this.LOD_LEVELS[i].distance) {
                        newLodLevel = Math.min(i + 2, 5); // Reduce detail
                        break;
                    }
                }
            }
            
            // Only recreate grid if LOD level changed
            if (newLodLevel !== patch.lodLevel) {
                patch.lodLevel = newLodLevel;
                patch.grid = new Grid(
                    this.LOD_LEVELS[newLodLevel].gridSize,
                    patch.centerX,
                    patch.centerY,
                    patch.size
                );
                patch.grid.initVAO(gl);
            }
        }
    }
    
    initVAO(gl: WebGL2RenderingContext): void {
        for (const { grid } of this.grids) {
            grid.initVAO(gl);
        }
    }
    
    draw(gl: WebGL2RenderingContext, wireframe: boolean = false): void {
        for (const patch of this.grids) {
            if (patch.visible) {
                patch.grid.draw(gl, wireframe);
            }
        }
    }
    
    getGridCount(): number {
        return this.grids.length;
    }
    
    getTotalVertexCount(): number {
        let total = 0;
        for (const { grid } of this.grids) {
            total += grid.getIndexCount() / 3;
        }
        return total;
    }
    
    /** Get statistics about current LOD distribution */
    getLODStats(): { [key: number]: number } {
        const stats: { [key: number]: number } = { 0: 0, 1: 0, 2: 0, 3: 0, 4: 0, 5: 0 };
        for (const patch of this.grids) {
            stats[patch.lodLevel]++;
        }
        return stats;
    }
}