不知道这里出现了什么错误。可以运行出来，但有错，望指正

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class JavaFXApplicationHeart extends Application {
@Override
public void start(Stage primaryStage) {
int width, height;
Canvas canvas = new Canvas(350, 350);
width = (int) canvas.getWidth();
height = (int) canvas.getHeight();
GraphicsContext gc = canvas.getGraphicsContext2D();
double x, y, r;
for (int i = 0; i <= 90; i++) {
for (int j = 0; j <= 90; j++) {
//转换为直角坐标系，设置偏移量，使图像居中
r = Math.PI / 45 * i * (1 - Math.sin(Math.PI / 45 * j)) * 19;
x = r * Math.cos(Math.PI / 45 * j) * Math.sin(Math.PI / 45 * i) + width / 2;
y = -r * Math.sin(Math.PI / 45 * j) + height / 4;
gc.setFill(Color.RED);
gc.fillOval(x, y, 2, 2);
gc.fillOval(x, y, 1, 1);
}
}
StackPane root = new StackPane();
root.getChildren().add(canvas);
Scene scene = new Scene(root, Color.BLACK);
primaryStage.setTitle("r=a(1-sinθ)");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}