ebiten/internal/graphics/math.go

// Copyright 2014 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package graphics

// minInternalImageSize is the minimum size of internal images (texture/framebuffer).
//
// For example, the image size less than 15 is not supported on some iOS devices.
// See also: https://stackoverflow.com/questions/15935651/certain-framebuffer-sizes-fail-on-ios-devices-gl-framebuffer-unsupported
const minInternalImageSize = 16

// InternalImageSize returns a nearest appropriate size as an internal image.
func InternalImageSize(x int) int {
	if x <= 0 {
		panic("graphics: x must be positive")
	}
	if x < minInternalImageSize {
		return minInternalImageSize
	}
	r := 1
	for r < x {
		r <<= 1
	}
	return r
}

func isInternalImageSize(x int) bool {
	if x <= 0 {
		return false
	}
	if x < minInternalImageSize {
		return false
	}
	return (x & (x - 1)) == 0
}