我正在创建一个地形网格,然后这个答案 https://stackoverflow.com/a/5284527/1356106我正在尝试将 CPU 计算法线迁移到基于着色器的版本,以便通过降低网格分辨率并使用在片段着色器中计算的法线贴图来提高性能。
我在用着MapBox高度图 https://docs.mapbox.com/help/troubleshooting/access-elevation-data/#mapbox-terrain-rgb用于地形数据。瓷砖看起来像这样:
每个像素的高程由以下公式给出:
const elevation = -10000.0 + ((red * 256.0 * 256.0 + green * 256.0 + blue) * 0.1);
我的原始代码首先创建一个密集网格(256*256 个正方形,由 2 个三角形组成),然后计算三角形和顶点法线。为了获得视觉上令人满意的结果,我将标高降低了 5000,以匹配场景中图块的宽度和高度(将来我将进行适当的计算以显示真实标高)。
我用这些简单的着色器绘图:
顶点着色器:
uniform mat4 u_Model;
uniform mat4 u_View;
uniform mat4 u_Projection;
attribute vec3 a_Position;
attribute vec3 a_Normal;
attribute vec2 a_TextureCoordinates;
varying vec3 v_Position;
varying vec3 v_Normal;
varying mediump vec2 v_TextureCoordinates;
void main() {
v_TextureCoordinates = a_TextureCoordinates;
v_Position = vec3(u_View * u_Model * vec4(a_Position, 1.0));
v_Normal = vec3(u_View * u_Model * vec4(a_Normal, 0.0));
gl_Position = u_Projection * u_View * u_Model * vec4(a_Position, 1.0);
}
片段着色器:
precision mediump float;
varying vec3 v_Position;
varying vec3 v_Normal;
varying mediump vec2 v_TextureCoordinates;
uniform sampler2D texture;
void main() {
vec3 lightVector = normalize(-v_Position);
float diffuse = max(dot(v_Normal, lightVector), 0.1);
highp vec4 textureColor = texture2D(texture, v_TextureCoordinates);
gl_FragColor = vec4(textureColor.rgb * diffuse, textureColor.a);
}
虽然速度很慢,但给出了视觉上令人满意的结果:
现在,我删除了所有基于 CPU 的法线计算代码,并用以下代码替换了我的着色器:
顶点着色器:
#version 300 es
precision highp float;
precision highp int;
uniform mat4 u_Model;
uniform mat4 u_View;
uniform mat4 u_Projection;
in vec3 a_Position;
in vec2 a_TextureCoordinates;
out vec3 v_Position;
out vec2 v_TextureCoordinates;
out mat4 v_Model;
out mat4 v_View;
void main() {
v_TextureCoordinates = a_TextureCoordinates;
v_Model = u_Model;
v_View = u_View;
v_Position = vec3(u_View * u_Model * vec4(a_Position, 1.0));
gl_Position = u_Projection * u_View * u_Model * vec4(a_Position, 1.0);
}
片段着色器:
#version 300 es
precision highp float;
precision highp int;
in vec3 v_Position;
in vec2 v_TextureCoordinates;
in mat4 v_Model;
in mat4 v_View;
uniform sampler2D u_dem;
uniform sampler2D u_texture;
out vec4 color;
const vec2 size = vec2(2.0,0.0);
const ivec3 offset = ivec3(-1,0,1);
float getAltitude(vec4 pixel) {
float red = pixel.x;
float green = pixel.y;
float blue = pixel.z;
return (-10000.0 + ((red * 256.0 * 256.0 + green * 256.0 + blue) * 0.1)) * 6.0; // Why * 6 and not / 5000 ??
}
void main() {
float s01 = getAltitude(textureOffset(u_dem, v_TextureCoordinates, offset.xy));
float s21 = getAltitude(textureOffset(u_dem, v_TextureCoordinates, offset.zy));
float s10 = getAltitude(textureOffset(u_dem, v_TextureCoordinates, offset.yx));
float s12 = getAltitude(textureOffset(u_dem, v_TextureCoordinates, offset.yz));
vec3 va = (vec3(size.xy, s21 - s01));
vec3 vb = (vec3(size.yx, s12 - s10));
vec3 normal = normalize(cross(va, vb));
vec3 transformedNormal = normalize(vec3(v_View * v_Model * vec4(normal, 0.0)));
vec3 lightVector = normalize(-v_Position);
float diffuse = max(dot(transformedNormal, lightVector), 0.1);
highp vec4 textureColor = texture(u_texture, v_TextureCoordinates);
color = vec4(textureColor.rgb * diffuse, textureColor.a);
}
现在它几乎立即加载,但有些问题:
- 在片段着色器中,我必须将高程乘以 6,而不是除以 5000,才能得到接近原始代码的值
- 结果不太好。特别是当我倾斜场景时,阴影非常暗(倾斜得越多,阴影就越暗):
你能找出造成这种差异的原因吗?
编辑:我创建了两个 JSFiddles:
- CPU 计算顶点法线的第一个版本:http://jsfiddle.net/tautin/tmugzv6a/10 http://jsfiddle.net/tautin/tmugzv6a/10
- 使用 GPU 计算法线贴图的第二个版本:http://jsfiddle.net/tautin/8gqa53e1/42 http://jsfiddle.net/tautin/8gqa53e1/42
当您使用倾斜滑块时会出现问题。