了解的drawRect或绘画实际上是如何在Android的协调工作

Question

我想在画布上绘制一个矩形，我现在面临的麻烦了解的Android的矩形绘制的深入。我读过的教程和每一个可能的，但我坚持。

在此图像中，红色矩形是我的目标。

无论任何矩形大小的我需要绘制底部的红色矩形位上方，并在矩形的中间。我对着这里的最糟糕的噩梦是理解的X，Y宽度和高度坐标。

任何人都可以解释，数学是如何工作的，有时我们上去，Y达到非常小，但相同的宽度坐标较高。而且我从来没有能够证明红内部矩形properly.In一些屏幕效果很好在其他一些失败。红色矩形有时会父矩形出来。

议程是要了解如何协调工作，确保内部红色矩形的完整性

这将是巨大的，我们将根据一个例子进行说明。我在用-

void drawRect(float left, float top, float right, float bottom, Paint paint)

绘制矩形

Answer 1

X水平上运行，从左边到右边。 Ÿ垂直延伸，从顶部到底部。这是完全一样的图形。所以（0/0）是在左上角。

当你走“向上” Y当然会越来越小，因为它从顶部增长到底部。

你必须要注意铺设出像列表视图元素，这些都将给出部分（或新的，你不能告诉）画布你的意见被绘制。这些意见将在自己的顶部/左侧位置具有为0x0。如果你需要绝对的，你必须继续调用View.getLocationOnScreen()并计算抵消自己。

Answer 2

canvas.drawRect(left,top,right,bottom,paint);

在这

1. 左：左侧矩形的从帆布的左侧的距离。
2. 顶部：从帆布的顶侧的矩形的顶壁的距离
3. 右：矩形的右侧从帆布的左侧的距离。
4. 底部：矩形的从帆布的顶侧的底侧的距离。

Answer 3

这将是有意义的。

float left = 100, top = 100; // basically (X1, Y1)

float right = left + 100; // width (distance from X1 to X2)
float bottom = top + 100; // height (distance from Y1 to Y2)

从而

RectF myRectum = new RectF(left, top, right, bottom);
canvas.drawRect(myRectum, myPaint);

Answer 4

这里是我的方法简单，易于

            int x = 100;  //position coordinate from left
            int y = 100;  //position coordinate from top
            int w = 100; //width of the rectangle
            int h = 100; //height of the rectangle
            drawRectangle(x, y, w, h, canvas, paint);

这里是我的功能

    public void drawRectangle(int left, int top, int right, int bottom, Canvas canvas, Paint paint) {
    right = left + right; // width is the distance from left to right
    bottom = top + bottom; // height is the distance from top to bottom
    canvas.drawRect(left, top, right, bottom, paint);
}

它工作得很好

Answer 5

希望我的笔记如下帮助你理解相对论属于矩形，帆布和视图。

/**
 * Rect holds four integer coordinates for a rectangle.
 * The rectangle is represented by the coordinates of its 4 edges (left, top, right bottom).
 * These fields can be accessed directly. Use width() and height() to retrieve the rectangle's width and height.
 *
 * Note that the right and bottom coordinates are exclusive.
 * This means a Rect being drawn untransformed onto a Canvas will draw into the column and row described by its left and top coordinates
 * , but not those of its bottom and right.
 *
 * With regard to calling to Canvas#drawRect(left,top,right,bottom,paint)
 *
 * left: Distance of the left side of rectangle from left side of canvas.
 * top: Distance of top side of rectangle from the top side of canvas
 * right: Distance of the right side of rectangle from left side of canvas.
 * bottom: Distance of the bottom side of rectangle from top side of canvas.
 * __________________________________
 *|
 *|
 *|   __l_______________________r__
 *|  |         view group A        |
 *| t|  0______________________w   |
 *|  |  | **** view group B *** |  |
 *|  |  | **** canvas of B **** |  |
 *|  |  | ********************* |  |
 *|  |  | ********************* |  |
 *|  |  | ********************* |  |
 *|  |  | ***** __________ **** |  |
 *|  |  | *****|## rect ##|**** |  |
 *|  |  | *****|##########|**** |  |
 *|  |  | *****|##########|**** |  |
 *|  |  | *****|##########|**** |  |
 *|  |  | *****|##########|**** |  |
 *|  |  | ***** ---------- **** |  |
 *|  |  | ********************* |  |
 *| b|  h-----------------------   |
 *|  |                             |
 *|  |                             |
 *|   -----------------------------
 *|
 * -----------------------------------
 *
 * 1. l, t, r, b are coordinates of view group B (PastryChart) relative to view group A (parent of PastryChart).
 * 2. The size of canvas of B is same as the size of the view group B
 *    , which means canvas of B is a canvas which the view group B is rendered to.
 * 3. The coordinates of rect is relative to a canvas, here is the canvas of B
 *    , which means the coordinates of rect going to represent child of view group B are relative to the canvas of B.
 *    ex. for a rect holding left = 0, the position of its left is located on the same position of the left of view group B
 *    ex. for a rect holding right = w, the position of its right is located on the same position of the right of view group B
 *    ex. for a rect holding top = 0, the position of its top is located on the same position of the top of view group B
 *    ex. for a rect holding bottom = h, the position of its bottom is located on the same position of the bottom of view group B
 * 4. The rect is used to stored the child measurement computed in measure pass
 *    for forward positioning child view (PastryView) in the layout pass taken by parent view (PastryChart).
 * 5. All of them are in pixels (px)
 */