OpenGL - Trying to add texture to triangle - c++

Question

I am trying to add a stop sign texture to a triangle in opengl.
But for some reason the image is coming up weird like I have the coordinates in the wrong order and the image is 1, mirrored and 2, not angled correctly:
I believe I set the texture coordinates correct but I am unsure. Have i got the texture coordinates in the wrong order?
Here is the code I have for it:
#include <glm\glm.hpp>
#include <graphics_framework.h>
#include <memory>
using namespace std;
using namespace graphics_framework;
using namespace glm;
mesh m;
effect eff;
target_camera cam;
texture tex;
bool load_content() {
// Construct geometry object
geometry geom;
// Create triangle data
// Positions
vector<vec3> positions{vec3(0.0f, 1.0f, 0.0f), vec3(-1.0f, -1.0f, 0.0f), vec3(1.0f, -1.0f, 0.0f)};
// *********************************
// Define texture coordinates for triangle
vector<vec2> tex_coords{ vec2(0.0f, 0.0f), vec2(1.0f, 0.0f), vec2(0.5f, 1.0f) };
// *********************************
// Add to the geometry
geom.add_buffer(positions, BUFFER_INDEXES::POSITION_BUFFER);
// *********************************
// Add texture coordinate buffer to geometry
geom.add_buffer(tex_coords, BUFFER_INDEXES::TEXTURE_COORDS_0);
// *********************************
// Create mesh object
m = mesh(geom);
// Load in texture shaders here
eff.add_shader("27_Texturing_Shader/simple_texture.vert", GL_VERTEX_SHADER);
eff.add_shader("27_Texturing_Shader/simple_texture.frag", GL_FRAGMENT_SHADER);
// *********************************
// Build effect
eff.build();
// Load texture "textures/sign.jpg"
tex = texture("textures/sign.jpg");
// *********************************
// Set camera properties
cam.set_position(vec3(10.0f, 10.0f, 10.0f));
cam.set_target(vec3(0.0f, 0.0f, 0.0f));
auto aspect = static_cast<float>(renderer::get_screen_width()) / static_cast<float>(renderer::get_screen_height());
cam.set_projection(quarter_pi<float>(), aspect, 2.414f, 1000.0f);
return true;
}
bool update(float delta_time) {
// Update the camera
cam.update(delta_time);
return true;
}
bool render() {
// Bind effect
renderer::bind(eff);
// Create MVP matrix
auto M = m.get_transform().get_transform_matrix();
auto V = cam.get_view();
auto P = cam.get_projection();
auto MVP = P * V * M;
// Set MVP matrix uniform
glUniformMatrix4fv(eff.get_uniform_location("MVP"), // Location of uniform
1, // Number of values - 1 mat4
GL_FALSE, // Transpose the matrix?
value_ptr(MVP)); // Pointer to matrix data
// *********************************
// Bind texture to renderer
renderer::bind(tex, 0);
// Set the texture value for the shader here
glUniform1i(eff.get_uniform_location("tex"), 0);
// *********************************
// Render the mesh
renderer::render(m);
return true;
}
void main() {
// Create application
app application("27_Texturing_Shader");
// Set load content, update and render methods
application.set_load_content(load_content);
application.set_update(update);
application.set_render(render);
// Run application
application.run();
}

Answer 1

That's because the order of your vertex positions and texture coordinates do not match. The first position is the top corner (assuming y is up), but the first texture coordinate is the bottom left corner of the image. Moving the last texture coordinate to the front should do the trick.
Your texture is probably mirrored along the y-axis. OpenGL expects the texture lines to be bottom-up, but most image libraries provide them top-down. Depends on what library you use to load the image. And of course, it will depend on the side from which you view the triangle.