如何在GLSL中创建纬度(水平)轮廓线? [英] How to create latitudinal (horizontal) contour lines in GLSL?

问题描述

我要达到这种效果:(仅水平轮廓线):

I'm aiming for this effect: (horizontal-only contour lines):

我确实找到了此示例，但是会创建水平和垂直轮廓线.我不太了解fwidth()的调用是如何生成行的.

I did find this example, however it creates horizontal and vertical contour lines. I can't quite wrap my head around how the call to fwidth() is generating the lines.

uniform float gsize;//size of the grid
uniform float gwidth;//grid lines'width in pixels
varying vec3 P;

void main()
{
    vec3 f  = abs(fract (P * gsize)-0.5);
    vec3 df = fwidth(P * gsize);
    float mi=max(0.0,gwidth-1.0), ma=max(1.0,gwidth);//should be uniforms
    vec3 g=clamp((f-df*mi)/(df*(ma-mi)),max(0.0,1.0-gwidth),1.0);//max(0.0,1.0-gwidth) should also be sent as uniform
    float c = g.x * g.y * g.z;
    gl_FragColor = vec4(c, c, c, 1.0);
    gl_FragColor = gl_FragColor * gl_Color;
}

我如何将该示例修改为仅水平线?

How would I modify that example to be horizontal-only lines?

有更好的解决方案吗?

更新:

来自以下修改的着色器的解决方案.仅使用y值使用浮点数.

Solution from modified shader below. Use floats using only the y value.

void main() {
            float f  = fract (_pos.y * 15.0);
            float df = fwidth(_pos.y * 15.0);

            float g = smoothstep(df * 1.0, df * 2.0, f);

            float c = g;

            gl_FragColor = vec4(c, c, c, 1.0);
    }

推荐答案

fwidth不能完全生成行，主要是fract是. fwidth仅用于在屏幕空间中保持线宽恒定.

fwidth is not exactly generating the lines, mainly fract is. fwidth is only used to keep the line width constant in screen space.

如果您尝试仅使用fract绘制1px线，它将起作用.但是，如果您想要宽线或抗锯齿线，则需要使用fwidth进行明智的插值.

If you try to draw 1px lines only using fract, it will work. But if you want wide lines or antialiased lines, you'll need fwidth to make sensible interpolations.

要只包含水平线，您可能只需要删除fract/fwidth计算中的坐标之一.尽管也许您应该首先从链接中尝试使用简单版本(更容易理解:D):

To only have horizontal lines, you probably just need to remove one of the coordinates in the fract/fwidth calculation. Although maybe you should try with the simple version first from your link (a lot easier to understand :D):

varying vec3 k;

void main()
{
    vec3 f  = fract (k * 100.0);
    vec3 df = fwidth(k * 100.0);

    vec3 g = smoothstep(df * 1.0, df * 2.0, f);

    float c = g.x * g.y * g.z;

    gl_FragColor = vec4(c, c, c, 1.0);
}

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