opengl won't overlap more than 1 texture - c++

Question

I'm trying to create an opengl program that creates a 2d square, and applies 2 textures on it.
I followed this tutorial: https://learnopengl.com/Getting-started/Textures
This is my fragment shader:
#version 330 core
//in vec3 Color;
in vec2 TexCoord;
out vec4 FragColor;
uniform sampler2D Texture1;
uniform sampler2D Texture2;
void main()
{
FragColor = mix(texture(Texture1, TexCoord), texture(Texture2, TexCoord), 0.5);
}
This is the code that sends the textures and the uniforms:
GLuint Tex1, Tex2;
int TexWidth, TexHeight, TexNrChannels;
unsigned char* TexData = stbi_load("container.jpg", &TexWidth, &TexHeight, &TexNrChannels, 0);
glGenTextures(1, &Tex1);
glBindTexture(GL_TEXTURE_2D, Tex1);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, TexWidth, TexHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, TexData);
glGenerateMipmap(GL_TEXTURE_2D);
glUniform1i(glGetUniformLocation(Program, "Texture1"), 0);
stbi_image_free(TexData);
TexData = stbi_load("awesomeface.png", &TexWidth, &TexHeight, &TexNrChannels, 0);
glGenTextures(1, &Tex2);
glBindTexture(GL_TEXTURE_2D, Tex2);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, TexWidth, TexHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, TexData);
glGenerateMipmap(GL_TEXTURE_2D);
glUniform1i(glGetUniformLocation(Program, "Texture2"), 1);
stbi_image_free(TexData);
And this is the render loop:
while (!glfwWindowShouldClose(window))
{
processInput(window);
// GL render here
glClearColor(0.05f, 0.0f, 0.1f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, Tex1);
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, Tex2);
glUseProgram(Program);
glBindVertexArray(VAO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glfwSwapBuffers(window);
glfwPollEvents();
}
When I run it, only the first texture shows up on the square, and the a argument (last argument) of the mix function in the shader won't make a difference for any value.
I tried activating (glActiveTexture + GlBindTexture) the second texture first in the render loop, and it caused the second texture to be shown exclusively.
How can I make the textures mix together like in the tutorial?
If this approach is wrong, I would like to learn about another way to accomplish the same result.

Answer 1

glUniform1i set a value in the default uniform block of the currently installed program. You have to install the program with glUseProgram, before you can set the value of a uniform variable:
GLint t1_loc = glGetUniformLocation(Program, "Texture1");
GLint t2_loc = glGetUniformLocation(Program, "Texture2");
glUseProgram(Program);
glUniform1i(t1_loc, 0);
glUniform1i(t2_loc, 1);
Alternatively you can use glProgramUniform1i:
glProgramUniform1i(Program, t1_loc, 0);
glProgramUniform1i(Program, t2_loc, 1);