1.缩放矩阵

#define PI 3.1415926

float Box(vec2 uv,vec2 bottomLeft,vec2 topRight,vec2 blur)
{
    vec2 c = smoothstep(bottomLeft,bottomLeft + blur,uv);
    vec2 co2 = smoothstep(topRight,topRight - blur ,uv);
    c *= co2;
    return c.x * c.y;
}

float crossShape(vec2 uv)
{
    float b1 = Box(uv,vec2(-0.3,-0.03),vec2(0.3,0.03),vec2(0.01,0.01));
    float b2 = Box(uv,vec2(-0.03,-0.3),vec2(0.03,0.3),vec2(0.01,0.01));
    return b1 + b2;
}

mat2 rotate2d(float angle)
{
    mat2 m = mat2(cos(angle),-sin(angle),sin(angle),cos(angle));
    return m;
}

mat2 globalScale(float scale)
{
    mat2 m = mat2(scale,0.0,
                    0.0,scale);
    return m;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = (fragCoord.xy - 0.5 * iResolution.xy) / iResolution.y;

    //旋转坐标系
    //uv -= vec2(0.1,0.1);
    float t = sin(iTime * 2.0) / (2.0 * PI) + 0.5;
    t *= 1.8;
    uv = globalScale(t) * uv;
    float c1 = crossShape(uv);

    fragColor = vec4(c1 * vec3(1.0,1.0,0.0),1.0);
}

效果:

2.缩放和旋转结合

#define PI 3.1415926

float Box(vec2 uv,vec2 bottomLeft,vec2 topRight,vec2 blur)
{
    vec2 c = smoothstep(bottomLeft,bottomLeft + blur,uv);
    vec2 co2 = smoothstep(topRight,topRight - blur ,uv);
    c *= co2;
    return c.x * c.y;
}

float crossShape(vec2 uv)
{
    float b1 = Box(uv,vec2(-0.3,-0.03),vec2(0.3,0.03),vec2(0.01,0.01));
    float b2 = Box(uv,vec2(-0.03,-0.3),vec2(0.03,0.3),vec2(0.01,0.01));
    return b1 + b2;
}

mat2 rotate2d(float angle)
{
    mat2 m = mat2(cos(angle),-sin(angle),sin(angle),cos(angle));
    return m;
}

mat2 globalScale(float scale)
{
    mat2 m = mat2(scale,0.0,
                    0.0,scale);
    return m;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = (fragCoord.xy - 0.5 * iResolution.xy) / iResolution.y;

    //旋转坐标系
    //uv -= vec2(0.1,0.1);
    float t = sin(iTime * 2.0) / (2.0 * PI) + 0.5;
    t *= 2.0;
    if(t < 1.0)
    {
        uv = rotate2d(iTime) * uv;
    }else{
        uv = globalScale(t) * uv;
    }

    float c1 = crossShape(uv);

    fragColor = vec4(c1 * vec3(1.0,1.0,0.0),1.0);
}

效果: