I'm wondering how I can erase from the rendertexture. e.g. I fill a rectangle and then want to make a circle in the center transparent again.
I tried drawing stuff with alpha 0 and using various blendmodes. I was actually looking for a BlendMode.None of some sort to copy the alpha channel directly, but there's only BlendMode.Normal, which doesn't seem to do the job.
Related
I am refering to a older question saying color blending with GDI+
Using GDI+ with Windows Forms, I want to be able to draw with a pen and blend color based on the destination pixel color.
For example, if I draw a line and it passes over black pixels, I want it to be a lighter color (like white for example) so that it's visible. When that same line passes over white pixels, it should be a darker color (black for example) so that it's still clearly visible.
the answers says to use a color matrix for transformation
so i started implementing it..
My image is present in raw data format in rgb48
Gdiplus::Bitmap image(input.width,input.height,input.width*6,PixelFormat48bppRGB,(unsigned char*)rgb48);
Gdiplus::Image *images= image.GetThumbnailImage(input.width,input.height);
Gdiplus::TextureBrush brush(images);
Gdiplus::Pen pen(&brush);
Gdiplus::ColorMatrix matrix={
-1.0f,0.0f,0.0f,0.0f,0.0f,
0.0f,-1.0f,0.0f,0.0f,0.0f,
0.0f,0.0f,-1.0f,0.0f,0.0f,
0.0f,0.0f,0.0f,1.0f,0.0f,
1.0f,1.0f,1.0f,0.0f,1.0f,
};
Gdiplus::Graphics gfx(&image1);
Gdiplus::ImageAttributes imageAttr;
imageAttr.SetColorMatrix(&matrix);
gfx.DrawImage(images,Gdiplus::Rect(0,0,input.width,input.height),0,0,1024,1024,Gdiplus::UnitPixel,&imageAttr);
I am not getting what i expect..Can some one help me in finding the mistake i m doing.
You can use the alpha component of a color to specify transparency, so that colors can be combined. However, if you want the combination to be something other than the alpha blend, you must draw the pixels yourself. You could first draw into a transparent bitmap, then render that onto the destination pixel by pixel.
I downloaded a icon, and now i want to reset the color of it, but i'm not good at photoshop, i've set the color of it to be red, but there are to many edges and corners, please tell me how to remove those edges by using photoshop step by step, thanks a lot.
here is the icon i downloaded:
and this is my ugly one:
The best way to alter a single color like this on a simple image such as this is to alter the Hue and Saturation [CTRL / CMD + U]...
This allows you greater color control and keeps the anti-aliased edges of the image intact.
Most beginners alter colors like this by simply selecting the color with the wand, or using the paint bucket on the color. Unfortunately this usually does one of 2 things:
Makes the ragged edges that you saw.
Leaves a halo of the old color as an orphan.
I did this in a few seconds with that tool:
In real life, transparency (or opacity) can be explained in a "simple" way by how much an object can reflect light, or how much of it pass through. So if an object is transparent light pass trough it, reflect on whatever is behind it and the light get back to us.
How computers simulate this behavior? I mean, we as developers, have many abstractions and APIs to set alpha levels and opacities of our pixels but how computers translates this into a bitmap to the screen?
What I think is happening: Both back and front colors are "combined" to result in a third color and this is then draw to screen. Eg: transparent white over back red on screen will be painted as pink!
Yes, you have it right. The "back" color is combined with the "front" color in proportion to the opacity of the front color.
For a single color channel, e.g. red, with opacity from 0 to 1:
new = old * (1 - opacity) + front * opacity
I have an image of size 480x800 pixels and there is a icon on one corner which I need to place. What I want is that to ignore all touches on the transparent areas and detect only the area where the icon is.
I found a solution in SO to this problem but it just tells the code to be used. I need to know exactly where to put that code since I am a beginner and don't know much about cocos2d so I expect a step by step solution.
Cocos2d 2.0 - Ignoring touches to transparent areas of layers/sprites
Do not use glReadPixels because it affected by bugs in android drivers. You can translate CCTouch to CCPoint in image coordinates using convertTouchToNodeSpace, and read image pixel at given point.
Create CCImage from file that contains semi-transparent picture, and read one pixel at tap point; it should be {0,0,0,0} for transparent area.
Don't forget to check that tap is not outside picture, and create pixel index in CCImage::getData() array with formulae unsigned index = x * imageWidth + y.
How to draw a transparent rectangle in j2me?
Transparency is supported only in immutable images, i.e. images loaded from files. So you can create appropriate image. Or create transparency via filling its transparency parts with background color.
Nokia has some functions that will allow you to draw transparent rects and polygons
http://www.developer.nokia.com/Resources/Library/Java/_zip/GUID-237420DE-CCBE-4A74-A129-572E0708D428/com/nokia/mid/ui/DirectGraphics.html
However if you want it to be a generic solution you should create a transparent image in code and draw it in the appropriate position. Create a int array with size = width*height then fill it with the required color (for example 0x550000ff for semi transparent blue) and create the image using Image.createRGBImage (and setting the last parameter to true).
int[] tmpArray = new int[width*height];
for(int i=tmpArray.length;i--!=0;)
tmpArray[i] = 0x550000ff;
Image transparentRectImg = Image.createRGBImage(tmpArray,width,height,true);
Also don't forget that some old j2me devices do not support alpha transparency even in images.