Question about load and render Wavefront OBJ with multi textures？

I have a Wavefront OBJ model with two texttures, like following.

Model.mtl
Model.obj
Model0_0000.png
Model1_0000.png

I can load the model successfully, but while I try to render the model, I can only get the render view with one texture. If i usetexture_0, I can get scene view with Model0_0000.png correctly. If i usetexture_1, I can get scene view with Model1_0000.png correctly. I can't get scene view with Model0_0000.png and Model1_0000.png together correctly.

I'm sure the obj file has no problem, because it can be rendered correctly by MeshLab and Open3D.

Do you have any advice? Thank you!

const std::string default_model_shader = R"Shader(
/////////////////////////////////////////
@start vertex
#version 120

#expect SHOW_COLOR
#expect SHOW_NORMAL
#expect SHOW_TEXTURE
#expect SHOW_MATCAP
#expect SHOW_UV

    uniform mat4 T_cam_norm;
    uniform mat4 KT_cw;
    attribute vec3 vertex;

#if SHOW_COLOR
    attribute vec4 color;
    varying vec4 vColor;
    void main() {
        vColor = color;
#elif SHOW_NORMAL
    attribute vec3 normal;
    varying vec3 vNormal;
    void main() {
        vNormal = mat3(T_cam_norm) * normal;
#elif SHOW_TEXTURE
    attribute vec2 uv;
    varying vec2 vUV;
    void main() {
        vUV = uv;
#elif SHOW_MATCAP
    attribute vec3 normal;
    varying vec3 vNormalCam;
    void main() {
        vNormalCam = mat3(T_cam_norm) * normal;
#elif SHOW_UV
    attribute vec2 uv;
    varying vec2 vUV;
    void main() {
        vUV = uv;
#else
    varying vec3 vP;
    void main() {
        vP = vertex;
#endif
        gl_Position = KT_cw * vec4(vertex, 1.0);
    }

/////////////////////////////////////////
@start fragment
#version 120
#expect SHOW_COLOR
#expect SHOW_NORMAL
#expect SHOW_TEXTURE
#expect SHOW_MATCAP
#expect SHOW_UV

#if SHOW_COLOR
    varying vec4 vColor;
#elif SHOW_NORMAL
    varying vec3 vNormal;
#elif SHOW_TEXTURE
    varying vec2 vUV;
    uniform sampler2D texture_0;
#elif SHOW_MATCAP
    varying vec3 vNormalCam;
    uniform sampler2D matcap;
#elif SHOW_UV
    varying vec2 vUV;
#else
    varying vec3 vP;
#endif

void main() {
#if SHOW_COLOR
    gl_FragColor = vColor;
#elif SHOW_NORMAL
    gl_FragColor = vec4((vNormal + vec3(1.0,1.0,1.0)) / 2.0, 1.0);
#elif SHOW_TEXTURE
    gl_FragColor = texture2D(texture_0, vUV);
#elif SHOW_MATCAP
    vec2 uv = 0.5 * vNormalCam.xy + vec2(0.5, 0.5);
    gl_FragColor = texture2D(matcap, uv);
#elif SHOW_UV
    gl_FragColor = vec4(vUV,1.0-vUV.x,1.0);
#else
    gl_FragColor = vec4(vP / 100.0,1.0);
#endif
}
)Shader";

stevenlovegrove / Pangolin

Question about load and render Wavefront OBJ with multi textures？ #808