问webgl 3D纹理从2D图像，工作，但与渲染问题

EN

<!-- FRAGMENT SHADER -->
<script id="fragment_shader1_custom3" type="x-shader/x-fragment">

uniform sampler2D texture;
uniform float imageIndex;
varying vec4 worldCoord;
varying vec2 vUv;

// tex is a texture with each slice of the cube placed in grid in a texture.
// texCoord is a 3d texture coord
// size is the size if the cube in pixels.
// slicesPerRow is how many slices there are across the texture
// numRows is the number of rows of slices

vec2 computeSliceOffset(float slice, float slicesPerRow, vec2 sliceSize) {
  return sliceSize * vec2(mod(slice, slicesPerRow),
  floor(slice / slicesPerRow));
}

vec4 sampleAs3DTexture(sampler2D tex, vec3 texCoord, float size, float numRows, float slicesPerRow){

  float slice   = texCoord.z * size;
  float sliceZ  = floor(slice);                         // slice we need
  float zOffset = fract(slice);                         // dist between slices

  vec2 sliceSize = vec2(1.0 / slicesPerRow,             // u space of 1 slice
    1.0 / numRows);                 // v space of 1 slice

  vec2 slice0Offset = computeSliceOffset(sliceZ, slicesPerRow, sliceSize);
  vec2 slice1Offset = computeSliceOffset(sliceZ + 1.0, slicesPerRow, sliceSize);

  vec2 slicePixelSize = sliceSize / size;               // space of 1 pixel
  vec2 sliceInnerSize = slicePixelSize * (size - 1.0);  // space of size pixels

  vec2 uv = slicePixelSize * 0.5 + texCoord.xy * sliceInnerSize;
  vec4 slice0Color = texture2D(tex, slice0Offset + uv);
  vec4 slice1Color = texture2D(tex, slice1Offset + uv);
  return mix(slice0Color, slice1Color, zOffset);
}


void main( void ) {
  // the position within the shader
  vec2 shaderPos = vUv;

  // if outside the texture cube, use a yellow color
  if(worldCoord.x < 0.0 || worldCoord.x >= 1.0 || worldCoord.y < 0.0 || worldCoord.y >= 1.0 || worldCoord.z < 0.0 || worldCoord.z >= 1.0){
    gl_FragColor = vec4(1.0, 1.0 , 0.0, 1.0);
  }else{

    vec3 chunkPosition = vec3(worldCoord.x, worldCoord.y, worldCoord.z);

    // 63.0 instead of 64.0 to avoid a edge situation
    gl_FragColor = sampleAs3DTexture(texture, chunkPosition, 63.0, 64.0, 1.0);

  }
}
</script> <!-- END FRAGMENT SHADER -->



<!-- VERTEX SHADER -->
<script id="vertexShader_custom1" type="x-shader/x-vertex">
varying vec2 vUv;
varying vec4 worldCoord;

void main()
{
  vUv = uv;
  vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );
  gl_Position = projectionMatrix * mvPosition;
  worldCoord = modelMatrix * vec4( position, 1.0 );
}
</script> <!-- END VERTEX SHADER -->