CImg Image is Colorless - c++

Question

Currently I am in the process of refining a function in my basic level editor program that allows me to save the maps I create. It spits out a .bmp image of the map produced. It does this through a library I've just discovered called CImg, which I know next to nothing about. Everything seems to work, but the resulting .bmp image is not colored, appearing instead in different shades of black and white. Like I said, I know basically nothing about the library, so if you know what the problem could be here, I would appreciate some help.
Here's the save function:
void Map::Save() {
Vertex top_left_most, top_right_most, bottom_left_most;
int img_w = 0, img_h = 0;
std::vector<std::pair<GLuint, GLuint>>::iterator tl = bufferIDs.begin(); //This little block gives the _most variables valid starting vals
glBindBuffer(GL_ARRAY_BUFFER, tl->second);
glGetBufferSubData(GL_ARRAY_BUFFER, sizeof(TextureCoord), sizeof(Vertex), &top_left_most);
top_right_most = bottom_left_most = top_left_most;
for (auto i = bufferIDs.begin(); i != bufferIDs.end(); ++i) { //SEEKS TOP LEFT MOST TILE ON MAP
Vertex current_coord;
glBindBuffer(GL_ARRAY_BUFFER, i->second);
glGetBufferSubData(GL_ARRAY_BUFFER, sizeof(TextureCoord), sizeof(Vertex), &current_coord);
if ((current_coord.x < top_left_most.x && current_coord.y < top_left_most.y) ||
(current_coord.x == top_left_most.x && current_coord.y < top_left_most.y) ||
(current_coord.x < top_left_most.x && current_coord.y == top_left_most.y)) {
top_left_most = current_coord;
}
}
for (auto i = bufferIDs.begin(); i != bufferIDs.end(); ++i) { //SEEKS TOP RIGHT MOST TILE ON MAP
Vertex current_coord;
glBindBuffer(GL_ARRAY_BUFFER, i->second);
glGetBufferSubData(GL_ARRAY_BUFFER, sizeof(TextureCoord), sizeof(Vertex), &current_coord);
if ((current_coord.x > top_right_most.x && current_coord.y < top_right_most.y) ||
(current_coord.x == top_right_most.x && current_coord.y < top_right_most.y) ||
(current_coord.x > top_right_most.x && current_coord.y == top_right_most.y)) {
top_right_most = current_coord;
}
}
for (auto i = bufferIDs.begin(); i != bufferIDs.end(); ++i) { //SEEKS BOTTOM LEFT MOST TILE ON MAP
Vertex current_coord;
glBindBuffer(GL_ARRAY_BUFFER, i->second);
glGetBufferSubData(GL_ARRAY_BUFFER, sizeof(TextureCoord), sizeof(Vertex), &current_coord);
if ((current_coord.x < bottom_left_most.x && current_coord.y > bottom_left_most.y) ||
(current_coord.x == bottom_left_most.x && current_coord.y > bottom_left_most.y) ||
(current_coord.x < bottom_left_most.x && current_coord.y == bottom_left_most.y)) {
bottom_left_most = current_coord;
}
}
img_w = (top_right_most.x + 64) - top_left_most.x; //Calculating image dimensions for the buffer
img_h = (bottom_left_most.y + 64) - top_left_most.y;
GLuint *image = new GLuint[img_w * img_h]; //Creating the image buffer
int int_start_x = 0; //start_x and y that will be used in buffer pointer positioning computations
int int_start_y = 0;
//these nested fors fill the buffer
for (GLfloat start_y = top_left_most.y; start_y != bottom_left_most.y + 64; start_y += 64) {
for (GLfloat start_x = top_left_most.x; start_x != top_right_most.x + 64; start_x += 64) {
bool in_map = false;
std::vector<std::pair<GLuint, GLuint>>::iterator valid_tile;
for (auto i = bufferIDs.begin(); i != bufferIDs.end(); ++i) { //This for checks to see if tile corresponding to start_x & y is present in map
Vertex current_tile_pos;
glBindBuffer(GL_ARRAY_BUFFER, i->second);
glGetBufferSubData(GL_ARRAY_BUFFER, sizeof(TextureCoord), sizeof(Vertex), &current_tile_pos);
if (current_tile_pos.x == start_x && current_tile_pos.y == start_y) {
in_map = true;
valid_tile = i;
break;
}
}
GLuint *imagepos = image; //Repositioning the pointer into the final image's buffer
imagepos += int_start_x + (int_start_y * img_w);
if (in_map) { //if in map, that tile's texture is used to fill the corresponding part of the image buffer
GLuint *texture = new GLuint[64 * 64];
glBindTexture(GL_TEXTURE_2D, valid_tile->first);
glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA, GL_UNSIGNED_BYTE, texture);
GLuint *texturepos = texture;
for (GLuint ypos = 0; ypos != 64; ++ypos) {
std::memcpy(imagepos, texturepos, 64 * 4);
texturepos += 64;
imagepos += img_w;
}
if (texture)
delete[] texture;
}
else { //otherwise, a default all-black array is used to fill the corresponding untiled part of the image buffer
GLuint *black_buffer = new GLuint[64 * 64];
GLuint *blackpos = black_buffer;
GLuint solid_black;
char *p = (char *)&solid_black;
p[0] = 0;
p[1] = 0;
p[2] = 0;
p[3] = 255;
for (GLuint i = 0; i != 64 * 64; ++i) {
black_buffer[i] = solid_black;
}
for (GLuint ypos = 0; ypos != 64; ++ypos) {
std::memcpy(imagepos, blackpos, 64 * 4);
blackpos += 64;
imagepos += img_w;
}
if (black_buffer)
delete[] black_buffer;
}
int_start_x += 64;
}
int_start_x = 0;
int_start_y += 64;
}
cimg_library::CImg<GLuint> final_image(image, img_w, img_h); //no color!!
final_image.save_bmp("map.bmp");
if (image)
delete[] image;
}
In case some explanation would be helpful, Vertex is a simple struct of two GLfloats (as is TextureCoord), bufferIDs is an std::vector of std::pairs of GLuints, the first representing a texture ID, and the second representing a VBO ID.
Here are the requested sample images:
what the image should look like (this is in monochrome)
Same exact image as above, but created using the reinterpret_cast method

Answer 1

Your line
cimg_library::CImg<GLuint> final_image(image, img_w, img_h);
is wrong if you are expecting a colour image because that creates a single channel image. You need a 3 at the end to make 3 channels - one for Red, one for Green and one for Blue.
Also, your data is stored in GLuint which means that a 4x2 pixel image will be stored like this, i.e. band-interleaved-by-pixel:
RGBA RGBA RGBA RGBA
RGBA RGBA RGBA RGBA
whereas CImg wants to store that in a band-interleaved-by-plane fashion:
RRRRRRRR
GGGGGGGG
BBBBBBBB
AAAAAAAA
This link explains the layout of CImg memory buffers.