Winforms C#渐变不透明度位图

问题描述

我想制作一个应用了线性不透明度的位图. (即，它在左侧更不透明，而在靠近右侧时逐渐变得不透明.)

I want to make a bitmap that has a linear opacity applied. (i.e. it is more opaque on the left side and get progressively less opaque as it approaches the right.)

这可能吗?我知道它可能具有恒定的不透明度级别.

Is this possible? I know its possible to have a constant opacity level.

推荐答案

因此，请不要使其保持不变，LinearGradientBrush可以轻松插值alpha值.设置了BackgroundImage的表单的简单演示:

So don't make it constant, LinearGradientBrush has no trouble interpolating the alpha value. A simple demonstration of a form that has the BackgroundImage set:

    protected override void OnPaint(PaintEventArgs e) {
        base.OnPaint(e);
        var rc = new Rectangle(20, 20, this.ClientSize.Width - 40, 50);
        using (var brush = new System.Drawing.Drawing2D.LinearGradientBrush(
            rc, 
            Color.FromArgb(255, Color.BlueViolet), 
            Color.FromArgb(0,   Color.BlueViolet), 
            0f)) {
                e.Graphics.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.Half;
                e.Graphics.FillRectangle(brush, rc);
        }
    }

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