Trying to render this code without using transformation concept

Question

I'm trying to change the position of triangle without using transformation function, By changing only the position of x each time,

this my code in main while loop

float MyPoints[] = { 0.1 , 0.2, 0.3, 0.4, 0.5 , 0.6, 0.7, 0.8, 0.9};
int offset = (-1, 1);
for (int i = 0; i < sizeof(MyPoints); i++) {
    offset += MyPoints[i];
    ourShader.Use();
    glBindVertexArray(VAO);
    glDrawArrays(GL_TRIANGLES, 0, 3);
    glBindVertexArray(0);// unbind
}

and this is in shader

out vec3 ourColor;
out vec2 TexCoord;
uniform vec4 offset;

void main() 
{
    gl_Position = vec4(position.x + offset, position.y, position.z, 1.0f);
    ourColor = color;
    TexCoord = texCoord;
} 

---

Edit

this my code in main while loop

    float offset = 1.0f;
    float step = 0.001f;  //move
    int i=0;
    // Loop until window closed (Game loop)
    while (!glfwWindowShouldClose(mainWindow))
    {
        // Get + Handle user input events
        glfwPollEvents();

        //Render
        // Clear the colorbuffer
        glClearColor(0.0f, 0.1f, 0.2f, 1.0f);
        //glPointSize(400.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // Call Shader Program
        //Rendering the first triangle

        GLuint program =ourShader.Program ; // program object from "ourShader"
        GLint  offset_loc = glGetUniformLocation(program, "offset");

        float MyPoints[] = { -0.1 , -0.2,-0.3,-0.4,-0.5 ,-0.6,-0.7,-0.8,-0.9 };

        int noPoints = sizeof(MyPoints) / sizeof(float);
        ourShader.Use();
        for (int i = 0; i < noPoints; i++) {
            glUniform1f(offset_loc, MyPoints[i] + offset);
        }
        offset += step;

        if (MyPoints[i] + offset >= 1.0f || MyPoints[i] + offset <= -1.0f)
            step *= -1.0f;

        //update uniform data

        glBindVertexArray(VAO);
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glfwSwapBuffers(mainWindow);
        glBindVertexArray(0);// unbind

    }

and this is in shader

out vec3 ourColor;
out vec2 TexCoord;
uniform float offset;

void main() 
{
    gl_Position = vec4(position.x + offset, position.y, position.z, 1.0f);
    ourColor = color;
    TexCoord = texCoord;
} 

the Edit code make an movement from (-1.0) till the middle to the end of the window

Answer 1

First of all the number of elements in the array is sizeof(MyPoints) / sizeof(float).

The type of the uniform variable offset has to be float:

uniform float offset;

You've to get the location of the uniform variable offset by glGetUniformLocation and to set the value of the uniform by e.g. glUniform1f:

GLuint program = ; // program object from "ourShader"
GLint  offset_loc = glGetUniformLocation(program, "offset");

float MyPoints[] = { 0.1 , 0.2, 0.3, 0.4, 0.5 , 0.6, 0.7, 0.8, 0.9};
int noPoints = sizeof(MyPoints) / sizeof(float);

// bind vertex array
glBindVertexArray(VAO);

// install program
ourShader.Use();

float offset = -1.0f;
for (int i = 0; i < noPoints; i++) {

    // set value of the uniform (after program is installed)
    offset += MyPoints[i];
    glUniform1f(offset_loc, offset);

    // draw one triangle
    glDrawArrays(GL_TRIANGLES, 0, 3);
}
glBindVertexArray(0);

---

If you want to make the triangles move, then you've to change the offset of each individual triangle in every frame. e.g.:

float offset = 0.0f;
float step = 0.01f;
while (!glfwWindowShouldClose(mainWindow))
{
    // [...]

    ourShader.Use();
    glUniform1f(offset_loc, offset);
    glDrawArrays(GL_TRIANGLES, 0, 3);

    // [...]

    // change offset
    offset += step;
    if (offset >= 1.0f || offset <= -1.0f)
        step *= -1.0f; // reverse direction
}