package main

import (
	"image"
	"image/color"
	"renderer2/hrend"
)

func Checkerboard(cols []color.Color, size int) image.Image {
	result := image.NewRGBA(image.Rect(0, 0, size, size))
	for y := range size {
		for x := range size {
			result.Set(x, y, cols[(x+y)%len(cols)])
		}
	}
	return result
}

func FlatTerrain(size int) *hrend.ObjModel {
	result := hrend.ObjModel{
		Vertices: make([]hrend.Vec3f, 0),
		VTexture: make([]hrend.Vec3f, 4),
		Faces:    make([]hrend.Facef, 0),
	}
	// For the simple square terrain, there aren't a lot of texture coords...
	result.VTexture[0] = hrend.Vec3f{X: 0, Y: 0, Z: 0}
	result.VTexture[1] = hrend.Vec3f{X: 1, Y: 0, Z: 0}
	result.VTexture[2] = hrend.Vec3f{X: 0, Y: 1, Z: 0}
	result.VTexture[3] = hrend.Vec3f{X: 1, Y: 1, Z: 0}
	// Generate all the simple vertices along the plane at y=0
	for z := -size; z <= size; z++ {
		for x := -size; x <= size; x++ {
			result.Vertices = append(result.Vertices, hrend.Vec3f{X: float32(x), Y: 0, Z: float32(z)})
		}
	}
	width := size + size + 1
	// Faces are slightly different; we generate two for every "cell" inside the vertices
	for z := 0; z < width-1; z++ {
		for x := 0; x < width-1; x++ {
			topleft := x + z*width
			topright := x + 1 + z*width
			bottomleft := x + (z+1)*width
			bottomright := x + 1 + (z+1)*width
			// remember to wind counter-clockwise
			result.Faces = append(result.Faces, hrend.Facef{
				hrend.Vertex{Pos: result.Vertices[topleft], Tex: result.VTexture[0]},
				hrend.Vertex{Pos: result.Vertices[bottomleft], Tex: result.VTexture[2]},
				hrend.Vertex{Pos: result.Vertices[topright], Tex: result.VTexture[1]},
			}, hrend.Facef{
				hrend.Vertex{Pos: result.Vertices[topright], Tex: result.VTexture[1]},
				hrend.Vertex{Pos: result.Vertices[bottomleft], Tex: result.VTexture[2]},
				hrend.Vertex{Pos: result.Vertices[bottomright], Tex: result.VTexture[3]},
			})
		}
	}
	return &result
}