Immediate mode texturing weird output - c++

Question

I'm trying to simply draw an image with OpenGL's immediate mode functions.
However, my output is kinda weird. I tried a few Texture parameters - but i get the same result, sometimes with different colors. I kinda can't figure out the problem, but i figure it's either the image loading or texture setup. I'll cut to the case, here is how i generate my texture (in a Texture2D class):
glBindTexture(GL_TEXTURE_2D, id);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
A call to glTexImage2D follows, like this: glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, _width, _height, 0, GL_RGB, GL_UNSIGNED_BYTE, data);, where data is an array of unsigned char set to 255, white. I then load a PNG file with CImg, like this:
CImg<unsigned char> image(_filename.c_str());
image.resize(m_Width, m_Height);
glBindTexture(GL_TEXTURE_2D, m_ID);
if(image.spectrum() == 4)
{
unsigned char* data = image.data();
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, m_Width, m_Height, GL_RGBA, GL_UNSIGNED_BYTE, data);
}
else if(image.spectrum() == 3)
{
unsigned char* data = image.data();
glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, m_Width, m_Height, GL_RGB, GL_UNSIGNED_BYTE, data);
}
glBindTexture(GL_TEXTURE_2D, 0);
But when i try to draw the texture in immediate mode like this (origin is upper left corner, notice the red rectangle arund the texture is intentional):
void SimpleRenderer::drawTexture(Texture2D* _texture, float _x, float _y, float _width, float _height)
{
_texture->setActive(0);
glBegin(GL_QUADS);
glTexCoord2f(0.0f, 0.0f);
glVertex2f(_x, _y);
glTexCoord2f(1.0f, 0.0f);
glVertex2f(_x + _width, _y);
glTexCoord2f(1.0f, 1.0f);
glVertex2f(_x + _width, _y + _height);
glTexCoord2f(0.0f, 1.0f);
glVertex2f(_x, _y + _height);
glEnd();
glBindTexture(GL_TEXTURE_2D, 0);
glColor3ub(strokeR, strokeG, strokeB);
glBegin(GL_LINE_LOOP);
glVertex2f((GLfloat)_x, (GLfloat)_y);
glVertex2f((GLfloat)_x+_width, (GLfloat)_y);
glVertex2f((GLfloat)_x+_width, (GLfloat)_y+_height);
glVertex2f((GLfloat)_x, (GLfloat)_y+_height);
glEnd();
}
I expect an output like this within the rectangle (debugging the same PNG within the same program/thread with CImg):
But i get this:
Can anyone spot the problem with my code?

Answer 1

From How pixel data are stored with CImg:
The values are not interleaved, and are ordered first along the X,Y,Z and V axis respectively (corresponding to the width,height,depth,dim dimensions), starting from the upper-left pixel to the bottom-right pixel of the instane image, with a classical scanline run.So, a color image with dim=3 and depth=1, will be stored in memory as :R1R2R3R4R5R6......G1G2G3G4G5G6.......B1B2B3B4B5B6.... (i.e following a 'planar' structure)and not as R1G1B1R2G2B2R3G3B3... (interleaved channels),
OpenGL does not work with planar data, it expects interleaved pixel data. Easiest solution is to use a library other than CImg.
This does not fix the scaling issues, but it's a good place to start.

Answer 2

Use CImg<T>::permute_axes() to transform your image buffer to interleaved format, like this :
CImg<unsigned char> img("imageRGB.png");
img.permute_axes("cxyz"); // Convert to interleaved representation
// Now, use img.data() here as a pointer for OpenGL functions.
img.permute_axes("yzcx"); // Go back to planar representation (if needed).
CImg is indeed a great library, so all these kind of transformations have been planned in the library.