IOS – OpenGL ES 绘制十字 GPUImageCrosshairGenerator

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//@Author:猿说编程
//@Blog(个人博客地址): www.codersrc.com
//@File:IOS – OpenGL ES 绘制十字 GPUImageCrosshairGenerator
//@Time:2022/04/18 07:30
//@Motto:不积跬步无以至千里，不积小流无以成江海，程序人生的精彩需要坚持不懈地积累！
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NSString *const kGPUImageCrosshairVertexShaderString = SHADER_STRING
(
 attribute vec4 position;

 uniform float crosshairWidth;

 varying vec2 centerLocation;
 varying float pointSpacing;

 void main()
 {
     gl_Position = vec4(((position.xy * 2.0) - 1.0), 0.0, 1.0);
     gl_PointSize = crosshairWidth + 1.0;
     pointSpacing = 1.0 / crosshairWidth;
     centerLocation = vec2(pointSpacing * ceil(crosshairWidth / 2.0), pointSpacing * ceil(crosshairWidth / 2.0));
 }
);

#if TARGET_IPHONE_SIMULATOR || TARGET_OS_IPHONE
NSString *const kGPUImageCrosshairFragmentShaderString = SHADER_STRING
(
 uniform lowp vec3 crosshairColor;

 varying highp vec2 centerLocation;
 varying highp float pointSpacing;

 void main()
 {
     lowp vec2 distanceFromCenter = abs(centerLocation - gl_PointCoord.xy);
     lowp float axisTest = step(pointSpacing, gl_PointCoord.y) * step(distanceFromCenter.x, 0.09) + step(pointSpacing, gl_PointCoord.x) * step(distanceFromCenter.y, 0.09);

     gl_FragColor = vec4(crosshairColor * axisTest, axisTest);
//     gl_FragColor = vec4(distanceFromCenterInX, distanceFromCenterInY, 0.0, 1.0);
 }
);
#else
NSString *const kGPUImageCrosshairFragmentShaderString = SHADER_STRING
(
 GPUImageEscapedHashIdentifier(version 120)\n

 uniform vec3 crosshairColor;

 varying vec2 centerLocation;
 varying float pointSpacing;

 void main()
 {
     vec2 distanceFromCenter = abs(centerLocation - gl_PointCoord.xy);
     float axisTest = step(pointSpacing, gl_PointCoord.y) * step(distanceFromCenter.x, 0.09) + step(pointSpacing, gl_PointCoord.x) * step(distanceFromCenter.y, 0.09);

     gl_FragColor = vec4(crosshairColor * axisTest, axisTest);
     //     gl_FragColor = vec4(distanceFromCenterInX, distanceFromCenterInY, 0.0, 1.0);
 }
);
#endif