Removed a divide-by-zero error in the soft light blend, caused by acc…

…ounting for premultiplied alpha.

framework/Source/GPUImageSoftLightBlendFilter.m

@@ -14,7 +14,8 @@ void main()
      mediump vec4 base = texture2D(inputImageTexture, textureCoordinate);
      mediump vec4 overlay = texture2D(inputImageTexture2, textureCoordinate2);
 
-     gl_FragColor = base * (overlay.a * (base / base.a) + (2.0 * overlay * (1.0 - (base / base.a)))) + overlay * (1.0 - base.a) + base * (1.0 - overlay.a);
+     lowp float alphaDivisor = base.a + step(base.a, 0.0); // Protect against a divide-by-zero blacking out things in the output
+     gl_FragColor = base * (overlay.a * (base / alphaDivisor) + (2.0 * overlay * (1.0 - (base / alphaDivisor)))) + overlay * (1.0 - base.a) + base * (1.0 - overlay.a);
  }
 );
 #else
@@ -31,7 +32,8 @@ void main()
      vec4 base = texture2D(inputImageTexture, textureCoordinate);
      vec4 overlay = texture2D(inputImageTexture2, textureCoordinate2);
 
-     gl_FragColor = base * (overlay.a * (base / base.a) + (2.0 * overlay * (1.0 - (base / base.a)))) + overlay * (1.0 - base.a) + base * (1.0 - overlay.a);
+     float alphaDivisor = base.a + step(base.a, 0.0); // Protect against a divide-by-zero blacking out things in the output
+     gl_FragColor = base * (overlay.a * (base / alphaDivisor) + (2.0 * overlay * (1.0 - (base / alphaDivisor)))) + overlay * (1.0 - base.a) + base * (1.0 - overlay.a);
  }
 );
 #endif