title: iPhone opengl es alpha-blending. I have black color in edge
body: <p>I am developing iPhone game. I have the below Source image to draw it to the background. The Source image has alpha 0x00 and gradation around edge and the background's alpha is 0xff. When I draw the source image to the background, I have black color like you could see the Result image. I am using OpenGL ES glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA) method. I have changed every possible arguments, but every time it is not moved. </p>
  
  <p>Why do I have the black color in the edge of the source image? What is the problem? Does not every games in iphone use gradation?</p>
  
  <p>Do I need to make the source image with out gradation?</p>
  
  <p>Does anyone know the solution?</p>
  
  <p>Source image : </p>
  
  <p><img src="https://i.stack.imgur.com/vSeKZ.png" alt="alt text"></p>
  
  <p>Result image : </p>
  
  <p><img src="https://i.stack.imgur.com/vUzzh.png" alt="alt text"></p>