Trying to render this code without using transformation concept - c++

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
}