跳到内容
CrossFly 是 100% 开源在 GitHub 关注我们
CrossFlyCrossFly
开始使用
全部示例
配方图片97 行 · 1 个文件

Images

Decode once, keep the Image, reuse it. Loading inside onPaint or inside a list's bind step is what makes scrolling stutter where the pictures are.

它展示了什么

Images, and the two questions that come up before the picture does.

How does it fill its box? ImageSize is the whole answer, and picking wrong is the most visible mistake in an app: a portrait photo stretched into a landscape tile is noticed by everybody and reported by nobody, because it looks like a bad photo rather than a bug. Cropping to fill is almost always right for a photo; fitting inside is almost always right for a logo.

Where does the image come from? An app's own assets, or bytes it was handed — a camera capture, a database blob, a download. Both end up as an Image, and neither belongs in onPaint: decoding is expensive, and doing it per frame is the classic reason a list stutters exactly where the pictures are.

Drawn here rather than loaded from a file, so the recipe carries no asset of its own — but a generated image and a decoded one behave identically from this point on.

在你的机器上运行

每个示例都是普通的 Window，启动器只需要它的名字。

gradlew lwjgl3:run --args="classname dev.cf.recipe.R26Images"
修改它

Java 是提前编译的，浏览器无法自行重建你的修改 —— 这里的代码在发布前已由 TeaVM 转成 JavaScript。把文件复制到项目里，它在四个平台上原样运行；上面那条命令就是全部准备工作。

正在此处运行CrossFly 0.1.32
正在启动应用…

由 TeaVM 编译为 JavaScript —— 是同一份代码，不是录像。 · 全部示例

它用到了什么

本示例触及的框架类型。带链接的有参考页。

CardColorUtilsComponentGapImageImageViewRelativeStylesWidgets

源码

完整无删减。这就是那个文件，不是片段。

原始
dev/cf/recipe/R26Images.java
package dev.cf.recipe;

import dev.crossfly.ui.*;
import dev.crossfly.ui.color.ColorUtils;
import dev.crossfly.ui.graphics.*;
import dev.crossfly.ui.image.Image;
import dev.crossfly.ui.layout.*;
import dev.crossfly.ui.style.*;

import static dev.crossfly.ui.Widgets.*;

/**
 * Images, and the two questions that come up before the picture does.
 *
 * <p><b>How does it fill its box?</b> {@link ImageView.ImageSize} is the whole answer, and picking
 * wrong is the most visible mistake in an app: a portrait photo stretched into a landscape tile is
 * noticed by everybody and reported by nobody, because it looks like a bad photo rather than a bug.
 * Cropping to fill is almost always right for a photo; fitting inside is almost always right for a
 * logo.</p>
 *
 * <p><b>Where does the image come from?</b> An app's own assets, or bytes it was handed — a camera
 * capture, a database blob, a download. Both end up as an {@link Image}, and neither belongs in
 * {@code onPaint}: decoding is expensive, and doing it per frame is the classic reason a list
 * stutters exactly where the pictures are.</p>
 *
 * <p>Drawn here rather than loaded from a file, so the recipe carries no asset of its own — but a
 * generated image and a decoded one behave identically from this point on.</p>
 */
public class R26Images extends Recipe
{
   public String title()
   {
      return "Images";
   }

   public String note()
   {
      return "Decode once, keep the Image, reuse it. Loading inside onPaint or inside a list's bind"
         + " step is what makes scrolling stutter where the pictures are.";
   }

   public void build(Component body) throws Exception
   {
      // Made once, held, reused by all three views below — the point of the recipe.
      Image swatch = gradient(240, 160);

      // The names repay one careful reading, because two of them are the opposite of what they
      // sound like. RATIO fits the whole picture INSIDE the box; FIT scales until it COVERS the
      // box and crops what hangs over. Guessing between those two is how a portrait photo ends up
      // letterboxed in a tile that had room to crop it properly.
      show(body, "RATIO — the whole picture, inside the box", swatch, ImageSize.RATIO);
      show(body, "FIT — covers the box, crops the overflow", swatch, ImageSize.FIT);
      show(body, "STRETCH — fills by distorting. Almost never right", swatch, ImageSize.STRETCH);
   }

   private void show(Component body, String caption, Image img, ImageSize size)
      throws Exception
   {
      Card c = new Card();
      c.add(LAY_AUTO, label(caption, 1f, true, Styles.textColor, Position.START));
      ImageView v = new ImageView(img, size);
      v.getStyle()
         .autoHeight(Relative.ofFont(6f));
      c.add(LAY_AUTO, outgap(v, 0, .4f, 0, 0));
      c.getStyle()
         .outgap(Gap.ofFont(0, 0, 0, .6f));
      body.add(LAY_AUTO, c);
   }

   /**
    * Builds an image in memory from the theme's own colours.
    *
    * <p>An {@code Image} is pixels; where they came from stops mattering the moment you have one.
    * The same object could have arrived from {@code PhotoPicker}, from a SQLite blob or from a
    * download, and every line after this one would be unchanged.</p>
    */
   private static Image gradient(int w, int h) throws Exception
   {
      Image img = Image.createSurface(w, h);
      int[] px = new int[w * h];
      int from = Styles.primaryColor.color(), to = tertiary().color();
      for (int y = 0; y < h; y++)
      {
         int rowColor = ColorUtils.lerpColor(from, to, y / (float) h);
         for (int x = 0; x < w; x++)
            // Diagonal bands, so cropping and stretching are both obvious at a glance.
            px[y * w + x] = ((x + y) / 18) % 2 == 0 ? rowColor
               : ColorUtils.lerpColor(rowColor, Styles.backColor.color(), .35f);
      }
      img.setPixels(px);
      // Pixels written, texture stale: applyChanges is what pushes them to the GPU. Forgetting it
      // gives you an image that is correct in memory and blank on screen.
      img.applyChanges();
      return img;
   }
}
给 AI 助手

本页的机器可读版本，让模型直接读取示例集，而不是猜测 API。

本示例（JSON）本示例（Markdown）
上一个A map with pins下一个Keyboard and focus