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 it's output scale value, not how that output value is used.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	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 and Description
static 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 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 DownsampleStrategy	CENTER_INSIDE Returns the original image if it is smaller than the target, otherwise it will be downscaled maintaining its original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other is less or equal than the requested size.
static 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 DownsampleStrategy	DEFAULT Default strategy, currently CENTER_OUTSIDE.
static 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 DownsampleStrategy	NONE Performs no downsampling or scaling.
static 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 and Description
DownsampleStrategy()

Method Summary

Modifier and Type	Method and 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 Detail

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, Downsampler treats this as equivalent to AT_MOST because only power of two downsampling can be used.

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.

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.

CENTER_INSIDE

public static final DownsampleStrategy CENTER_INSIDE

Returns the original image if it is smaller than the target, otherwise it will be downscaled maintaining its original aspect ratio, so that one of the image's dimensions is exactly equal to the requested size and the other is less or equal than the requested size.

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

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 Detail

DownsampleStrategy

public DownsampleStrategy()

Method Detail

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.