使用 3D 纹理时结果不正确 [英] Incorrect result when using 3D textures

问题描述

我使用的是现代 OpenGL 4.3 核心.

I'm using modern OpenGL 4.3 core.

我刚刚意识到 1024p x 1024p 图块集对于我的需要来说太小了.所以，我用 1024p x 1024p x 4p 3D 纹理替换了它.(我知道，这不是最好的解决方案，我最好使用 2D 纹理数组.我只是想知道为什么我当前的解决方案不起作用.)

I just realized that 1024p x 1024p tileset is too small for my needs. So, I replaced it with 1024p x 1024p x 4p 3D texture. (I know, it's not the best solution, and I better to use 2D texture array. I'm just wondering why my current solution doesn't work.)

x 和 y 纹理坐标工作正常，和以前一样.z 也可以使用，但有点不正确.我希望第一层有 z == 0.0，第二层 - z == 0.3333333，第三层 - z == 0.66666666 和第四个 - z == 1.0.

x and y texture coordinates work fine, same as before. z also work, but a bit incorrectly. I would expect the 1st layer to have z == 0.0, 2nd layer - z == 0.3333333, 3rd layer - z == 0.66666666 and 4rd one - z == 1.0.

第 1 层和第 4 层按预期工作.但是 0.33333333 和 0.66666666 给了我错误的结果:
0.33333333 -> 第一层与第二层混合
0.66666666 -> 第 3 层与第 4 层混合
(我使用的是线性过滤，这就是它们混合在一起的原因.)

The 1st and 4th layers work as expected. But 0.33333333 and 0.66666666 give me incorrect results:
0.33333333 -> 1st layer mixed with 2nd layer
0.66666666 -> 3rd layer mixed with 4th layer
(I'm using linear filtering, that's why they mix together.)

我尝试为第 2 层和第 3 层选择正确的 z 值:
当 z == 0.38
时，第二个显示正常当 z == 0.62
时，第三个显示正常(当然，这些数字是近似值.)

I tried to pick the right z values for 2nd and 3rd layers:
2nd displays fine when z == 0.38
3rd displays fine when z == 0.62
(These numbers are approximate, of course.)

任何想法为什么会发生这种情况以及我如何解决这个问题?

Any ideas why this happen and how I can fix this?

这就是我创建纹理的方式:

This is how I create the texture:

glActiveTexture(GL_TEXTURE1);
glGenTextures(1, &maintex);
glBindTexture(GL_TEXTURE_3D, maintex);
glTexImage3D(GL_TEXTURE_3D, 0, GL_RGBA8, TEXSIZE, TEXSIZE, 4, 0, GL_RGBA, GL_UNSIGNED_BYTE, textemp);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_3D, GL_TEXTURE_WRAP_R, GL_CLAMP_TO_EDGE);

这是我的着色器:

const char *vertex = 1+R"(
#version 430
uniform layout(location = 3) vec2 fac;
in layout(location = 0) vec2 vpos; // vertex coords
in layout(location = 1) vec3 tpos; // texture coords
in layout(location = 2) vec4 c_off;  // color offset    = vec4(0,0,0,0) by default
in layout(location = 3) vec4 c_mult; // color multiplicator    = vec4(1,1,1,1) by default
// These two are used to do some sort of gamma correction 

out vec3 var_tpos;
out vec4 var_c_off;
out vec4 var_c_mult;
void main()
{
    var_tpos = tpos;
    var_c_off = c_off;
    var_c_mult = c_mult;
    gl_Position = vec4(vpos.x * fac.x - 1, vpos.y * fac.y + 1, 0, 1);
})";


const char *fragment = 1+R"(
#version 430
uniform layout(location = 0) sampler3D tex;
in vec3 var_tpos;
in vec4 var_c_off;
in vec4 var_c_mult;
out vec4 color;
void main()
{
    color = texture(tex, vec3(var_tpos.x / 1024, var_tpos.y / 1024, var_tpos.z));
    color.x *= var_c_mult.x;
    color.y *= var_c_mult.y;
    color.z *= var_c_mult.z;
    color.w *= var_c_mult.w;
    color   += var_c_off;
})";

推荐答案

那是因为 0 是左纹素的最左边"部分，而 1 是最右边纹素的最右边点.假设我们有 4 个纹素，坐标如下:

That's because 0 is the "leftmost" part of the left texel and 1 is the rightmost point in the rightmost texel. Assume we have 4 texels, than the coordinates are as follows:

0       1/4      1/2      3/4       1
|  tx1   |  tx2   |  tx3   |  tx4   |

由于您需要准确地击中体素的中心，因此您必须使用比预期高 1/2 体素的地址 (+0.25/2 = +0.125)，因此体素中心如底部所述下图的线.

since you need to hit exactly the center of a voxel, you have to use addresses that are 1/2 voxel higher then you expected (+0.25/2 = +0.125), thus the voxel centers are as described in the bottom line of the following diagram.

|  tx1   |  tx2   |  tx3   |  tx4   |
    |        |        |        |
  0.125    0.375     0.625    0.875

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