Package com.bumptech.glide.load.resource.bitmap

Class DownsampleStrategy

java.lang.Object

com.bumptech.glide.load.resource.bitmap.DownsampleStrategy

public abstract class DownsampleStrategy
extends Object

Indicates the algorithm to use when downsampling images.

DownsampleStrategy does not provide any guarantees about output sizes. Behavior will differ depending on the ResourceDecoder using the strategy and the version of Android the code runs on. Use DownsampleStrategy as an optimization to improve memory efficiency only. If you need a particular size or shape output, use an Transformation either instead or in addition to a DownsampleStrategy.

Some differences between versions of Android and ResourceDecoders are listed below, but the list is not comprehensive because DownsampleStrategy only controls its output scale value, not how that output value is used.

On some versions of Android, precise scaling is not possible. In those cases, the strategies can only pick between downsampling to between 1x the requested size and 2x the requested size and between 0.5x the requested size and 1x the requested size because only power of two downsampling is supported. To preserve the potential for a Transformation to scale precisely without a loss in quality, all but AT_MOST will prefer to downsample to between 1x and 2x the requested size.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static enum	DownsampleStrategy.SampleSizeRounding	Indicates whether to prefer to prefer downsampling or scaling to prefer lower memory usage or higher quality.

Field Summary

Fields

Modifier and Type	Field	Description
static final DownsampleStrategy	AT_LEAST	Downsamples so the image's smallest dimension is between the given dimensions and 2x the given dimensions, with no size restrictions on the image's largest dimension.
static final DownsampleStrategy	AT_MOST	Downsamples so the image's largest dimension is between 1/2 the given dimensions and the given dimensions, with no restrictions on the image's smallest dimension.
static final DownsampleStrategy	CENTER_INSIDE	Identical to FIT_CENTER, but never upscales.
static final DownsampleStrategy	CENTER_OUTSIDE	Scales, maintaining the original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other dimension is greater than or equal to the requested size.
static final DownsampleStrategy	DEFAULT	Default strategy, currently CENTER_OUTSIDE.
static final DownsampleStrategy	FIT_CENTER	Scales, maintaining the original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other dimension is less than or equal to the requested size.
static final DownsampleStrategy	NONE	Performs no downsampling or scaling.
static final Option<DownsampleStrategy>	OPTION	Indicates the DownsampleStrategy option that will be used to calculate the sample size to use to downsample an image given the original and target dimensions of the image.

Constructor Summary

Constructors

Constructor	Description
DownsampleStrategy()

Method Summary

Modifier and Type	Method	Description
abstract DownsampleStrategy.SampleSizeRounding	getSampleSizeRounding(int sourceWidth, int sourceHeight, int requestedWidth, int requestedHeight)	Returns a non-null DownsampleStrategy.SampleSizeRounding to use to resolve rounding errors and conflicts between scaling for the width and the height of the image.
abstract float	getScaleFactor(int sourceWidth, int sourceHeight, int requestedWidth, int requestedHeight)	Returns a float (0, +infinity) indicating a scale factor to apply to the source width and height when displayed in the requested width and height.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

AT_LEAST

public static final DownsampleStrategy AT_LEAST

Downsamples so the image's smallest dimension is between the given dimensions and 2x the given dimensions, with no size restrictions on the image's largest dimension.

Does not upscale if the requested dimensions are larger than the original dimensions.

AT_MOST

public static final DownsampleStrategy AT_MOST

Downsamples so the image's largest dimension is between 1/2 the given dimensions and the given dimensions, with no restrictions on the image's smallest dimension.

Does not upscale if the requested dimensions are larger than the original dimensions.

FIT_CENTER

public static final DownsampleStrategy FIT_CENTER

Scales, maintaining the original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other dimension is less than or equal to the requested size.

This method will upscale if the requested width and height are greater than the source width and height. To avoid upscaling, use AT_LEAST, AT_MOST or CENTER_INSIDE.

On pre-KitKat devices, FIT_CENTER will downsample by a power of two only so that one of the image's dimensions is greater than or equal to the requested size. No guarantees are made about the second dimensions. This is NOT the same as AT_LEAST because only one dimension, not both, are greater than or equal to the requested dimensions, the other may be smaller.

CENTER_INSIDE

public static final DownsampleStrategy CENTER_INSIDE

Identical to FIT_CENTER, but never upscales.

CENTER_OUTSIDE

public static final DownsampleStrategy CENTER_OUTSIDE

Scales, maintaining the original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other dimension is greater than or equal to the requested size.

This method will upscale if the requested width and height are greater than the source width and height. To avoid upscaling, use AT_LEAST, AT_MOST, or CENTER_INSIDE.

On pre-KitKat devices, Downsampler treats this as equivalent to AT_LEAST because only power of two downsampling can be used.

NONE

public static final DownsampleStrategy NONE

Performs no downsampling or scaling.

DEFAULT

public static final DownsampleStrategy DEFAULT

Default strategy, currently CENTER_OUTSIDE.

OPTION

public static final Option<DownsampleStrategy> OPTION

Indicates the DownsampleStrategy option that will be used to calculate the sample size to use to downsample an image given the original and target dimensions of the image.

Constructor Details

DownsampleStrategy

public DownsampleStrategy()

Method Details

getScaleFactor

public abstract float getScaleFactor(int sourceWidth,
 int sourceHeight,
 int requestedWidth,
 int requestedHeight)

Returns a float (0, +infinity) indicating a scale factor to apply to the source width and height when displayed in the requested width and height.

The returned scale factor will be split into a power of two sample size applied via BitmapFactory.Options.inSampleSize and a float scale factor applied after downsampling via BitmapFactory.Options.inTargetDensity and BitmapFactory.Options.inDensity. Because of rounding errors the scale factor may not be applied precisely.

The float scaling factor will only be applied on KitKat+. Prior to KitKat, only the power of two downsampling will be applied.

Parameters:

sourceWidth - The width in pixels of the image to be downsampled.

sourceHeight - The height in pixels of the image to be downsampled.

requestedWidth - The width in pixels of the view/target the image will be displayed in.

requestedHeight - The height in pixels of the view/target the image will be displayed in.

getSampleSizeRounding

public abstract DownsampleStrategy.SampleSizeRounding getSampleSizeRounding(int sourceWidth,
 int sourceHeight,
 int requestedWidth,
 int requestedHeight)

Returns a non-null DownsampleStrategy.SampleSizeRounding to use to resolve rounding errors and conflicts between scaling for the width and the height of the image.

Parameters:

sourceWidth - The width in pixels of the image to be downsampled.

sourceHeight - The height in pixels of the image to be downsampled.

requestedWidth - The width in pixels of the view/target the image will be displayed in.

requestedHeight - The height in pixels of the view/target the image will be displayed in.