我想在android maps api版本2中绘制折线。我希望它有很多颜色，最好是渐变色。在我看来，折线只允许单色。我怎样才能做到这一点？我已经有api-v1叠加绘制我喜欢的东西，所以我可以重用一些代码
public class RouteOverlayGoogle extends Overlay {
public void draw(Canvas canvas, MapView mapView, boolean shadow) {
//(...) draws line with color representing speed
}
我知道已经有很长一段时间了，但是仍然没有渐变多段线（截至写作，〜可能2015年）并且绘制多条折线确实没有切割它（锯齿状边缘，相当多的滞后时间）处理几百个点，只是在视觉上没有吸引力）。
当我必须实现渐变折线时，我最终做的是实现一个TileOverlay，它将折线渲染到画布然后光栅化它（请参阅我要写的具体代码的要点https://gist.github.com/Dagothig/5f9cf0a4a7a42901a7b2）。
该实现不会尝试进行任何类型的视口剔除，因为我最终不需要它来达到我想要的性能（我不确定数字，但是每个瓷砖的时间不到一秒，多个瓷砖将是同时渲染）。
渲染渐变折线可能非常棘手，因为你正在处理不同的视口（位置和大小）：更重要的是，我在高缩放级别（20+）的浮点精度限制下遇到了一些问题。最后我没有使用缩放和从画布翻译功能，因为我会得到奇怪的腐败问题。
如果你使用类似的数据结构（纬度，经度和时间戳）需要多个段来正确渲染渐变（我最终一次使用3个点），需要注意的其他事项。
为了后人的缘故，我还要把这些代码留在这里:(如果你想知道https://github.com/googlemaps/android-maps-utils来自哪里，那么投影是用com.google.maps.android.projection.SphericalMercatorProjection完成的）
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.Shader;
import com.google.android.gms.maps.model.LatLng;
import com.google.android.gms.maps.model.Tile;
import com.google.android.gms.maps.model.TileProvider;
import com.google.maps.android.SphericalUtil;
import com.google.maps.android.geometry.Point;
import com.google.maps.android.projection.SphericalMercatorProjection;
import java.io.ByteArrayOutputStream;
import java.util.List;
/**
* Tile overlay used to display a colored polyline as a replacement for the non-existence of gradient
* polylines for google maps
*/
public class ColoredPolylineTileOverlay<T extends ColoredPolylineTileOverlay.PointHolder> implements TileProvider {
public static final double LOW_SPEED_CLAMP_KMpH = 0;
public static final double LOW_SPEED_CLAMP_MpS = 0;
// TODO: calculate speed as highest speed of pointsCollection
public static final double HIGH_SPEED_CLAMP_KMpH = 50;
public static final double HIGH_SPEED_CLAMP_MpS = HIGH_SPEED_CLAMP_KMpH * 1000 / (60 * 60);
public static final int BASE_TILE_SIZE = 256;
public static int[] getSpeedColors(Context context) {
return new int[] {
context.getResources().getColor(R.color.polyline_low_speed),
context.getResources().getColor(R.color.polyline_med_speed),
context.getResources().getColor(R.color.polyline_high_speed)
};
}
public static float getSpeedProportion(double metersPerSecond) {
return (float)(Math.max(Math.min(metersPerSecond, HIGH_SPEED_CLAMP_MpS), LOW_SPEED_CLAMP_MpS) / HIGH_SPEED_CLAMP_MpS);
}
public static int interpolateColor(int[] colors, float proportion) {
int rTotal = 0, gTotal = 0, bTotal = 0;
// We correct the ratio to colors.length - 1 so that
// for i == colors.length - 1 and p == 1, then the final ratio is 1 (see below)
float p = proportion * (colors.length - 1);
for (int i = 0; i < colors.length; i++) {
// The ratio mostly resides on the 1 - Math.abs(p - i) calculation :
// Since for p == i, then the ratio is 1 and for p == i + 1 or p == i -1, then the ratio is 0
// This calculation works BECAUSE p lies within [0, length - 1] and i lies within [0, length - 1] as well
float iRatio = Math.max(1 - Math.abs(p - i), 0.0f);
rTotal += (int)(Color.red(colors[i]) * iRatio);
gTotal += (int)(Color.green(colors[i]) * iRatio);
bTotal += (int)(Color.blue(colors[i]) * iRatio);
}
return Color.rgb(rTotal, gTotal, bTotal);
}
protected final Context context;
protected final PointCollection<T> pointsCollection;
protected final int[] speedColors;
protected final float density;
protected final int tileDimension;
protected final SphericalMercatorProjection projection;
// Caching calculation-related stuff
protected LatLng[] trailLatLngs;
protected Point[] projectedPts;
protected Point[] projectedPtMids;
protected double[] speeds;
public ColoredPolylineTileOverlay(Context context, PointCollection pointsCollection) {
super();
this.context = context;
this.pointsCollection = pointsCollection;
speedColors = getSpeedColors(context);
density = context.getResources().getDisplayMetrics().density;
tileDimension = (int)(BASE_TILE_SIZE * density);
projection = new SphericalMercatorProjection(BASE_TILE_SIZE);
calculatePointsAndSpeeds();
}
public void calculatePointsAndSpeeds() {
trailLatLngs = new LatLng[pointsCollection.getPoints().size()];
projectedPts = new Point[pointsCollection.getPoints().size()];
projectedPtMids = new Point[Math.max(pointsCollection.getPoints().size() - 1, 0)];
speeds = new double[Math.max(pointsCollection.getPoints().size() - 1, 0)];
List<T> points = pointsCollection.getPoints();
for (int i = 0; i < points.size(); i++) {
T point = points.get(i);
LatLng latLng = point.getLatLng();
trailLatLngs[i] = latLng;
projectedPts[i] = projection.toPoint(latLng);
// Mids
if (i > 0) {
LatLng previousLatLng = points.get(i - 1).getLatLng();
LatLng latLngMid = SphericalUtil.interpolate(previousLatLng, latLng, 0.5);
projectedPtMids[i - 1] = projection.toPoint(latLngMid);
T previousPoint = points.get(i - 1);
double speed = SphericalUtil.computeDistanceBetween(latLng, previousLatLng) / ((point.getTime() - previousPoint.getTime()) / 1000.0);
speeds[i - 1] = speed;
}
}
}
@Override
public Tile getTile(int x, int y, int zoom) {
// Because getTile can be called asynchronously by multiple threads, none of the info we keep in the class will be modified
// (getTile is essentially side-effect-less) :
// Instead, we create the bitmap, the canvas and the paints specifically for the call to getTile
Bitmap bitmap = Bitmap.createBitmap(tileDimension, tileDimension, Bitmap.Config.ARGB_8888);
// Normally, instead of the later calls for drawing being offset, we would offset them using scale() and translate() right here
// However, there seems to be funky issues related to float imprecisions that happen at large scales when using this method, so instead
// The points are offset properly when drawing
Canvas canvas = new Canvas(bitmap);
Matrix shaderMat = new Matrix();
Paint gradientPaint = new Paint();
gradientPaint.setStyle(Paint.Style.STROKE);
gradientPaint.setStrokeWidth(3f * density);
gradientPaint.setStrokeCap(Paint.Cap.BUTT);
gradientPaint.setStrokeJoin(Paint.Join.ROUND);
gradientPaint.setFlags(Paint.ANTI_ALIAS_FLAG);
gradientPaint.setShader(new LinearGradient(0, 0, 1, 0, speedColors, null, Shader.TileMode.CLAMP));
gradientPaint.getShader().setLocalMatrix(shaderMat);
Paint colorPaint = new Paint();
colorPaint.setStyle(Paint.Style.STROKE);
colorPaint.setStrokeWidth(3f * density);
colorPaint.setStrokeCap(Paint.Cap.BUTT);
colorPaint.setStrokeJoin(Paint.Join.ROUND);
colorPaint.setFlags(Paint.ANTI_ALIAS_FLAG);
// See https://developers.google.com/maps/documentation/android/views#zoom for handy info regarding what zoom is
float scale = (float)(Math.pow(2, zoom) * density);
renderTrail(canvas, shaderMat, gradientPaint, colorPaint, scale, x, y);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
return new Tile(tileDimension, tileDimension, baos.toByteArray());
}
public void renderTrail(Canvas canvas, Matrix shaderMat, Paint gradientPaint, Paint colorPaint, float scale, int x, int y) {
List<T> points = pointsCollection.getPoints();
double speed1, speed2;
MutPoint pt1 = new MutPoint(), pt2 = new MutPoint(), pt3 = new MutPoint(), pt1mid2 = new MutPoint(), pt2mid3 = new MutPoint();
// Guard statement: if the trail is only 1 point, just render the point by itself as a speed of 0
if (points.size() == 1) {
pt1.set(projectedPts[0], scale, x, y, tileDimension);
speed1 = 0;
float speedProp = getSpeedProportion(speed1);
colorPaint.setStyle(Paint.Style.FILL);
colorPaint.setColor(interpolateColor(speedColors, speedProp));
canvas.drawCircle((float) pt1.x, (float) pt1.y, colorPaint.getStrokeWidth() / 2f, colorPaint);
colorPaint.setStyle(Paint.Style.STROKE);
return;
}
// Guard statement: if the trail is exactly 2 points long, just render a line from A to B at d(A, B) / t speed
if (points.size() == 2) {
pt1.set(projectedPts[0], scale, x, y, tileDimension);
pt2.set(projectedPts[1], scale, x, y, tileDimension);
speed1 = speeds[0];
float speedProp = getSpeedProportion(speed1);
drawLine(canvas, colorPaint, pt1, pt2, speedProp);
return;
}
// Because we want to be displaying speeds as color ratios, we need multiple points to do it properly:
// Since we use calculate the speed using the distance and the time, we need at least 2 points to calculate the distance;
// this means we know the speed for a segment, not a point.
// Furthermore, since we want to be easing the color changes between every segment, we have to use 3 points to do the easing;
// every line is split into two, and we ease over the corners
// This also means the first and last corners need to be extended to include the first and last points respectively
// Finally (you can see about that in getTile()) we need to offset the point projections based on the scale and x, y because
// weird display behaviour occurs
for (int i = 2; i < points.size(); i++) {
pt1.set(projectedPts[i - 2], scale, x, y, tileDimension);
pt2.set(projectedPts[i - 1], scale, x, y, tileDimension);
pt3.set(projectedPts[i], scale, x, y, tileDimension);
// Because we want to split the lines in two to ease over the corners, we need the middle points
pt1mid2.set(projectedPtMids[i - 2], scale, x, y, tileDimension);
pt2mid3.set(projectedPtMids[i - 1], scale, x, y, tileDimension);
// The speed is calculated in meters per second (same format as the speed clamps); because getTime() is in millis, we need to correct for that
speed1 = speeds[i - 2];
speed2 = speeds[i - 1];
float speed1Prop = getSpeedProportion(speed1);
float speed1to2Prop = getSpeedProportion((speed1 + speed2) / 2);
float speed2Prop = getSpeedProportion(speed2);
// Circle for the corner (removes the weird empty corners that occur otherwise)
colorPaint.setStyle(Paint.Style.FILL);
colorPaint.setColor(interpolateColor(speedColors, speed1to2Prop));
canvas.drawCircle((float)pt2.x, (float)pt2.y, colorPaint.getStrokeWidth() / 2f, colorPaint);
colorPaint.setStyle(Paint.Style.STROKE);
// Corner
// Note that since for the very first point and the very last point we don't split it in two, we used them instead.
drawLine(canvas, shaderMat, gradientPaint, colorPaint, i - 2 == 0 ? pt1 : pt1mid2, pt2, speed1Prop, speed1to2Prop);
drawLine(canvas, shaderMat, gradientPaint, colorPaint, pt2, i == points.size() - 1 ? pt3 : pt2mid3, speed1to2Prop, speed2Prop);
}
}
/**
* Note: it is assumed the shader is 0, 0, 1, 0 (horizontal) so that it lines up with the rotation
* (rotations are usually setup so that the angle 0 points right)
*/
public void drawLine(Canvas canvas, Matrix shaderMat, Paint gradientPaint, Paint colorPaint, MutPoint pt1, MutPoint pt2, float ratio1, float ratio2) {
// Degenerate case: both ratios are the same; we just handle it using the colorPaint (handling it using the shader is just messy and ineffective)
if (ratio1 == ratio2) {
drawLine(canvas, colorPaint, pt1, pt2, ratio1);
return;
}
shaderMat.reset();
// PS: don't ask me why this specfic orders for calls works but other orders will mess up
// Since every call is pre, this is essentially ordered as (or my understanding is that it is):
// ratio translate -> ratio scale -> scale to pt length -> translate to pt start -> rotate
// (my initial intuition was to use only post calls and to order as above, but it resulted in odd corruptions)
// Setup based on points:
// We translate the shader so that it is based on the first point, rotated towards the second and since the length of the
// gradient is 1, then scaling to the length of the distance between the points makes it exactly as long as needed
shaderMat.preRotate((float) Math.toDegrees(Math.atan2(pt2.y - pt1.y, pt2.x - pt1.x)), (float)pt1.x, (float)pt1.y);
shaderMat.preTranslate((float)pt1.x, (float)pt1.y);
float scale = (float)Math.sqrt(Math.pow(pt2.x - pt1.x, 2) + Math.pow(pt2.y - pt1.y, 2));
shaderMat.preScale(scale, scale);
// Setup based on ratio
// By basing the shader to the first ratio, we ensure that the start of the gradient corresponds to it
// The inverse scaling of the shader means that it takes the full length of the call to go to the second ratio
// For instance; if d(ratio1, ratio2) is 0.5, then the shader needs to be twice as long so that an entire call (1)
// Results in only half of the gradient being used
shaderMat.preScale(1f / (ratio2 - ratio1), 1f / (ratio2 - ratio1));
shaderMat.preTranslate(-ratio1, 0);
gradientPaint.getShader().setLocalMatrix(shaderMat);
canvas.drawLine(
(float)pt1.x,
(float)pt1.y,
(float)pt2.x,
(float)pt2.y,
gradientPaint
);
}
public void drawLine(Canvas canvas, Paint colorPaint, MutPoint pt1, MutPoint pt2, float ratio) {
colorPaint.setColor(interpolateColor(speedColors, ratio));
canvas.drawLine(
(float)pt1.x,
(float)pt1.y,
(float)pt2.x,
(float)pt2.y,
colorPaint
);
}
public interface PointCollection<T extends PointHolder> {
List<T> getPoints();
}
public interface PointHolder {
LatLng getLatLng();
long getTime();
}
public static class MutPoint {
public double x, y;
public MutPoint set(Point point, float scale, int x, int y, int tileDimension) {
this.x = point.x * scale - x * tileDimension;
this.y = point.y * scale - y * tileDimension;
return this;
}
}
}
请注意，此实现假定两个相对较大的事情：
我认为处理（1）不会很困难。但是，如果您打算以这种方式绘制多条折线，您可能需要查看一些方法来增强性能（保持折线的边界框能够轻松地丢弃那些不适合视口的折线）。
关于使用TileOverlay还要记住的另一件事是，它是在完成移动后渲染的，而不是在渲染过程中渲染的。因此，您可能需要使用其下方的实际单色折线来备份叠加层，以使其具有一定的连续性。
PS：这是我第一次尝试回答问题，所以如果有什么我应该修复或做的不同请告诉我。
一个简单的解决方案：绘制多条折线并单独设置颜色。