I have a few lines of code that add a plant into my canvas game:
我有几行代码将植物添加到我的画布游戏中:
function drawPlant() {
base_image = new Image();
base_image.src = 'http://i.imgur.com/xOupnQp.png';
if (treeLoaded) {
ctx.drawImage(base_image, 20, 333, 60, base_image.height * (60/base_image.width));
}
else {
base_image.onload = function(){
treeLoaded = true;
};
}
This puts the image into my game. However, I also want to make it faded out a bit. Could I use GlobalAlpha for this? And if so, how do I do it? Thanks.
这会将图像放入我的游戏中。但是,我也想让它淡出一点。我可以使用GlobalAlpha吗?如果是这样,我该怎么做?谢谢。
1 个解决方案
#1
Yes, globalAlpha
is a good choice. It takes a value in the range [0, 1].
是的,globalAlpha是一个不错的选择。它取一个[0,1]范围内的值。
For example:
(example also corrects loading pattern)
(例子也纠正了加载模式)
function drawPlant() {
base_image = new Image();
base_image.onload = function(){
treeLoaded = true;
ctx.globalAlpha = 0.5; // 50% opacity
ctx.drawImage(this, 20, 333, 60, base_image.height * (60/base_image.width));
ctx.globalAlpha = 1; // normal full opacity
};
base_image.src = 'http://i.imgur.com/xOupnQp.png';
}
You might want to consider a callback too as loading images happens asychronously, for example, a modified example with callback-ability could look like:
您可能也想考虑回调,因为加载图像是异步发生的,例如,具有回调能力的修改示例可能如下所示:
function drawPlant(callback) {
base_image = new Image();
base_image.onload = function(){
treeLoaded = true;
ctx.globalAlpha = 0.5; // 50% opacity
ctx.drawImage(this, 20, 333, 60, base_image.height * (60/base_image.width));
ctx.globalAlpha = 1; // normal full opacity
callback(this); // invoke callback with image as argument
};
base_image.src = 'http://i.imgur.com/xOupnQp.png';
}
Then:
drawPlant(function(img) {
// continue from here...
});
#1
Yes, globalAlpha
is a good choice. It takes a value in the range [0, 1].
是的,globalAlpha是一个不错的选择。它取一个[0,1]范围内的值。
For example:
(example also corrects loading pattern)
(例子也纠正了加载模式)
function drawPlant() {
base_image = new Image();
base_image.onload = function(){
treeLoaded = true;
ctx.globalAlpha = 0.5; // 50% opacity
ctx.drawImage(this, 20, 333, 60, base_image.height * (60/base_image.width));
ctx.globalAlpha = 1; // normal full opacity
};
base_image.src = 'http://i.imgur.com/xOupnQp.png';
}
You might want to consider a callback too as loading images happens asychronously, for example, a modified example with callback-ability could look like:
您可能也想考虑回调,因为加载图像是异步发生的,例如,具有回调能力的修改示例可能如下所示:
function drawPlant(callback) {
base_image = new Image();
base_image.onload = function(){
treeLoaded = true;
ctx.globalAlpha = 0.5; // 50% opacity
ctx.drawImage(this, 20, 333, 60, base_image.height * (60/base_image.width));
ctx.globalAlpha = 1; // normal full opacity
callback(this); // invoke callback with image as argument
};
base_image.src = 'http://i.imgur.com/xOupnQp.png';
}
Then:
drawPlant(function(img) {
// continue from here...
});