defer image loading

src/components/grid.tsx

@@ -6,6 +6,7 @@ import * as React from "react";
 export interface Props {
   images: Model.Image[];
   onImageSelected: (image: Model.Image) => void;
+  pageBottom: number;
   width: number;
 }
 
@@ -20,7 +21,11 @@ interface Row {
 export class Grid extends React.PureComponent<Props, {}> {
   static displayName = "Grid";
 
+  private gridHeight = 0;
+
   render() {
+    this.gridHeight = 0;
+
     let row: Model.Image[] = [];
     const rows: Row[] = [];
     let rowWidth = 0;
@@ -57,9 +62,15 @@ export class Grid extends React.PureComponent<Props, {}> {
             onClick={() => this.props.onImageSelected(image)}
             key={image.src}
             width={(image.width / image.height) * height}
+            defer={
+              this.gridHeight > this.props.pageBottom + 2 * this._rowHeight()
+            }
           />
         );
       });
+
+      this.gridHeight += height;
+
       return (
         <div
           className="Grid-row"

src/components/image_set.tsx

@@ -6,24 +6,43 @@ import * as React from "react";
 export interface Props {
   imageSet: Model.ImageSet;
   onImageSelected: (img: Model.Image) => void;
+  setGridHeight: (height: number) => void;
+  pageBottom: number;
   width: number;
 }
 
 export class ImageSet extends React.PureComponent<Props, {}> {
   static displayName = "ImageSet";
 
+  private divRef: React.RefObject<HTMLDivElement> = React.createRef();
+
   render() {
     return (
-      <div className="ImageSet">
+      <div className="ImageSet" ref={this.divRef}>
         <h2>
           {this.props.imageSet.location} · {this.props.imageSet.description}
         </h2>
         <Grid
           images={this.props.imageSet.images}
           onImageSelected={this.props.onImageSelected}
+          pageBottom={this.props.pageBottom}
           width={this.props.width}
         />
       </div>
     );
   }
+
+  componentDidMount() {
+    this._setGridHeight();
+  }
+
+  componentDidUpdate() {
+    this._setGridHeight();
+  }
+
+  private _setGridHeight = () => {
+    if (this.divRef.current) {
+      this.props.setGridHeight(this.divRef.current.clientHeight);
+    }
+  };
 }

src/components/picture.tsx

@@ -6,6 +6,11 @@ export interface Props {
   image: Model.Image;
   onClick: () => void;
   width: number;
+  defer?: boolean;
+}
+
+export interface State {
+  hasLoadedOnce: boolean;
 }
 
 interface SrcSetInfo {
@@ -13,10 +18,29 @@ interface SrcSetInfo {
   bestSrc: string;
 }
 
-export class Picture extends React.PureComponent<Props, {}> {
+export class Picture extends React.PureComponent<Props, State> {
   static displayName = "Picture";
 
+  state: State = {
+    hasLoadedOnce: false
+  };
+
+  static getDerivedStateFromProps(props: Props, state: State): State | null {
+    return !state.hasLoadedOnce && !props.defer
+      ? { hasLoadedOnce: true }
+      : null;
+  }
+
   render() {
+    if (this.props.defer && !this.state.hasLoadedOnce) {
+      return (
+        <div
+          className="Picture-defer"
+          style={{ width: this.props.width + "px" }}
+        />
+      );
+    }
+
     const srcSet = this._srcset();
 
     return (

src/components/root.tsx

@@ -9,13 +9,19 @@ export interface Props {}
 export interface State {
   data?: Model.Data | null;
   selectedImage?: Model.Image | null;
+  gridHeights: number[];
+  pageBottom: number;
   width: number;
 }
 
 export class Root extends React.PureComponent<Props, State> {
   static displayName = "Root";
 
+  private imageSetRefs: React.RefObject<ImageSet>[] = [];
+
   state: State = {
+    gridHeights: [],
+    pageBottom: window.innerHeight + window.pageYOffset,
     width: window.innerWidth
   };
 
@@ -27,19 +33,22 @@ export class Root extends React.PureComponent<Props, State> {
       .then(this._loadHash)
       .catch(e => console.error("Error fetching data", e));
 
-    window.onresize = () => {
-      this.setState({ width: window.innerWidth });
-    };
+    window.onresize = this._onViewChange;
+    window.onscroll = this._onViewChange;
 
     window.onpopstate = this._loadHash;
   }
 
   render() {
     const imageSets = this.state.data
-      ? this.state.data.sets.map(set => (
+      ? this.state.data.sets.map((set, idx) => (
           <ImageSet
             key={set.location + set.description}
             imageSet={set}
+            pageBottom={
+              this.state.pageBottom - this._getPreviousGridHeights(idx)
+            }
+            setGridHeight={this._setGridHeight(idx)}
             onImageSelected={this._onImageSelected}
             width={this.state.width}
           />
@@ -82,6 +91,13 @@ export class Root extends React.PureComponent<Props, State> {
     }
   };
 
+  private _onViewChange = () => {
+    this.setState({
+      pageBottom: window.innerHeight + window.pageYOffset,
+      width: window.innerWidth
+    });
+  };
+
   private _onImageSelected = (img: Model.Image) => {
     this.setState({ selectedImage: img });
     window.history.pushState(null, "", `#${img.src}`);
@@ -91,4 +107,19 @@ export class Root extends React.PureComponent<Props, State> {
     this.setState({ selectedImage: null });
     window.history.pushState(null, "", "#");
   };
+
+  private _setGridHeight = (grid: number) => (height: number) => {
+    if (this.state.gridHeights[grid] === height) {
+      return;
+    }
+    this.setState(state => {
+      const newGridHeights = [...state.gridHeights];
+      newGridHeights[grid] = height;
+
+      return { gridHeights: newGridHeights };
+    });
+  };
+
+  private _getPreviousGridHeights = (grid: number): number =>
+    this.state.gridHeights.slice(0, grid).reduce((a, b) => a + b, 0);
 }