gradient | 易学教程

Four point gradient in iOS

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问题 I am planing to create a four point gradient, pictured below, by drawing two linear gradients via core graphics and masking between them with a third black and white linear gradient. Is there a more efficient way to draw a four point gradient using core graphics, or other? 回答1: You can save the mask gradient when you use a CGBlendMode. It's just harder to control the exact colors. But if that's not important for you, it could be a little more efficient in terms of lines of code and maybe also

How can you create a CSS3 gradient in Opera?

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问题 I can create CSS gradients in IE6/7/8/9/FF3.6+ and Chrome (see below). My question is: How would one create a gradient in Opera? .gradient{ /*Mozilla Firefox 3.6*/ background-image: -moz-linear-gradient(top, #dcdcdc, #c6c6c6); /*Webkit aka Google Chrome*/ background-image: -webkit-gradient(linear,left bottom,left top,color-stop(0, #c6c6c6),color-stop(1, #dcdcdc)); /*Internet Explorer 6,7 and 8*/ filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#dcdcdc', endColorstr='#c6c6c6')

How to interpolate hue values in HSV colour space?

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问题 I'm trying to interpolate between two colours in HSV colour space to produce a smooth colour gradient. I'm using a linear interpolation, eg: h = (1 - p) * h1 + p * h2 s = (1 - p) * s1 + p * s2 v = (1 - p) * v1 + p * v2 (where p is the percentage, and h1, h2, s1, s2, v1, v2 are the hue, saturation and value components of the two colours) This produces a good result for s and v but not for h. As the hue component is an angle, the calculation needs to work out the shortest distance between h1

Fade image to transparent like a gradient

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I would like to have an image (a background image) to fade to transparent so that content behind it can actually be seen (barely, thanks to transparency). I can achieve it obviously with a PNG image, but I need to ask to my graphic designer to change the image every time I want to change the start => stop transparency points (maybe I want more color or maybe I want less color and more transparency). Are there any chance I can achieve the same effect with CSS3? I tried applying a gradient to transparent on a jpg (and a png) but I can't see through it unless the PNG has already transparency (and

Machine learning - Linear regression using batch gradient descent

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I am trying to implement batch gradient descent on a data set with a single feature and multiple training examples ( m ). When I try using the normal equation, I get the right answer but the wrong one with this code below which performs batch gradient descent in MATLAB. function [theta] = gradientDescent(X, y, theta, alpha, iterations) m = length(y); delta=zeros(2,1); for iter =1:1:iterations for i=1:1:m delta(1,1)= delta(1,1)+( X(i,:)*theta - y(i,1)) ; delta(2,1)=delta(2,1)+ (( X(i,:)*theta - y(i,1))*X(i,2)) ; end theta= theta-( delta*(alpha/m) ); computeCost(X,y,theta) end end y is the

How to convert x,y coordinates to an angle?

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问题 Microsoft provide an excellent SVG gradient maker so IE9 can also have "CSS3" gradients (click Custom). I currently utilise their logic for my Fireworks and Dreamweaver extensions to convert gradients to SVG, but I only know how to do it for standard top, bottom, left, right directions. If you enter an angle, I don't do the conversion, because I'm not sure how I would convert x1, x2, y1, y2 to CSS3 angle degrees. The gradient generator provides values like this: x1="0%" y1="0%" x2="56

Generating gradients programmatically?

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Given 2 rgb colors and a rectangular area, I'd like to generate a basic linear gradient between the colors. I've done a quick search and the only thing I've been able to find is this blog entry , but the example code seems to be missing, or at least it was as of this posting. Anything helps, algorithms, code examples, whatever. This will be written in Java, but the display layer is already taken care of, I just need to figure out how to figure out what to display. Konrad Rudolph you want an interpolation between the first and the second colour. Interpolating colours is easy by calculating the

How do I calculate a four colour gradient?

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问题 If I have four colours (A, B, C & D) on four corners of a square and I want to fill that square with a gradient that blends nicely between the four colours how would I calculate the colour of the point E? The closer E is to any of the other points, the strong that colour should affect the result. Any idea how to do that? Speed and simplicity is preferred to accuracy. colours http://rabien.com/image/colours.png 回答1: The best solution when a gradient is required between two colors, is to use

iPhone iOS how to add linear gradient to a UIButton under the button's text or image?

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问题 I'm working on creating fancy looking UIbuttons by adding linear gradient to the button. However I'm not sure at which index I need to add the gradient. The code that I have currently places the gradient over the image/text. How can I insert a sublayer to a UIButton under the text/image sublayer? It is important for me to keep the text and the image of a button visible! +(void)addLinearGradientToView:(UIView*)view TopColor:(UIColor*)topColor BottomColor:(UIColor*)bottomColor { for(CALayer*

How to animate gradient?

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问题 How to animate gradient from color#1 to color#2? Something similar to I'm planning to use it as health-bar for unit (so, it will be finit animation starting with green and ending with red) 回答1: While googling it, I found 2 ways to do it for android: use ShaderFactory or extends View, using new Shader(new LinearGradient()) . Both answers do the same - calling new Shader() every View.onDraw(Canvas canvas) method's call. Its really expensive if number of such animated gradients more than ~3. So