three.js - 片段着色器基础 - 根据片段的位置为片段着色

Question

我尝试根据片段在最高和最低顶点之间的位置为着色器中的片段着色。以下是着色器：

<script type="x-shader/x-vertex" id="vertexshader">

    uniform     float   span;

    attribute   float   displacement;

    varying     vec3    vNormal;
    varying     float   color_according_to_z;

                float   z_actual;

    void main() {
        vNormal = normal;

        vec3 newPosition = position + normal * vec3(0.0, 0.0, displacement);
        gl_Position = projectionMatrix * modelViewMatrix * vec4(newPosition, 1.0);

        z_actual = gl_Position.z + span / 2.0;
        color_according_to_z = 1.0 / span * z_actual;
    }

</script>

<script type="x-shader/x-fragment" id="fragmentshader">

    uniform     float   span;

    varying     float   color_according_to_z;

    void main()
    {
        gl_FragColor = vec4(color_according_to_z, 0.5, 0.5, 1.0);
    }

</script>

这是我的渲染函数：

function render() {
    requestAnimationFrame(render);

    plane.rotation.x = global_x_rotation;
    plane.rotation.z = global_z_rotation;

    for(var i = attributes.displacement.value.length - 1; i >= 0; i--) {
        attributes.displacement.value[i] = attributes.displacement.value[i] - 0.5 + Math.random();
    };

    uniforms.lowest = attributes.displacement.value.min();
    uniforms.highest = attributes.displacement.value.max();
    uniforms.span = uniforms.highest - uniforms.lowest;

    attributes.displacement.needsUpdate = true;

    uniforms.lowest.needsUpdate = true;
    uniforms.highest.needsUpdate = true;
    uniforms.span.needsUpdate = true;

    renderer.render(scene, camera);
}

我在帧之间更改位移并重新计算最高和最低顶点之间的跨度。

最后一块，如何根据片段的最高或最低位置来绘制片段，我还想不通。

Here is a jsfiddle with the mentioned code.

Answer 1

您有几个我可以看到的错误。检查变量中的 NaN。

着色器逻辑看起来不错，但它可能无法产生您想要的颜色。

var max = -1.0e30;
var min = +1.0e30;
var x;
for(var i = attributes.displacement.value.length - 1; i >= 0; i--) {
    x = attributes.displacement.value[i] += - 0.5 + Math.random();
    if (x < min ) min = x;
    if (x > max ) max = x;
};

uniforms.lowest.value = min; // lowest.value !
uniforms.highest.value = max;
uniforms.span.value = max - min;

attributes.displacement.needsUpdate = true;

//uniforms.lowest.needsUpdate = true; // not needed for uniforms
//uniforms.highest.needsUpdate = true;
//uniforms.span.needsUpdate = true;

小提琴：http://jsfiddle.net/c2jry/2/