Texture colors replaced by purple tones - opengl

Question

I try to display a texture on a quad but the colors was replaced by some purple.
The code is inspired from "learnopengl" website but I didn't find what I failed.
Here the shaders.
vertSrc:cstring = """
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;
out vec2 texCoord;
uniform mat4 projection;
void main()
{
gl_Position = projection * vec4(aPos, 1.0f);
texCoord = aTexCoord;
}
"""
fragSrc:cstring = """
#version 330 core
out vec4 FragColor;
in vec2 texCoord;
uniform sampler2D matTexture;
void main()
{
FragColor = texture(matTexture, texCoord);
}
"""
The opengl code for the texture.
glGenTextures(1, addr textureID)
glBindTexture(GL_TEXTURE_2D, textureID)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texWidth, texHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, addr imageData[0])
glGenerateMipmap(GL_TEXTURE_2D)
The image loading thanks to the stb_image library.
var
textureID:OGLuint
texWidth:OGLint
texHeight:OGLint
channelCount:OGLint
imageData = stbi_load("Test/2d-rendering-test./stack.png", addr texWidth, addr texHeight, addr channelCount, 0)
And the opengl code in the main loop.
glBindTexture(GL_TEXTURE_2D, textureID)
If you are curious here a complete nim file who displays the issue.
https://bitbucket.org/Neotry/2d-rendering-test./src/master/WIPtest.nim

Answer 1

The Portable Network Graphics (PNG) file may contain 32-bit RGBA colors.
Force the stbi_load to generate an image with 4 color channels, by explicitly pass 4 to the last parameter:
imageData = stbi_load("Test/2d-rendering-test./stack.png",
addr texWidth, addr texHeight, addr channelCount, 4)
See stb_image.h:
Basic usage (see HDR discussion below for HDR usage):
int x,y,n;
unsigned char *data = stbi_load(filename, &x, &y, &n, 0);
// ... process data if not NULL ...
// ... x = width, y = height, n = # 8-bit components per pixel ...
// ... replace '0' with '1'..'4' to force that many components per pixel
// ... but 'n' will always be the number that it would have been if you said 0
stbi_image_free(data)
Finally the format parameter of glTexImage2D has to be GL_RGBA or GL_BGRA. For the internal format can be kept GL_RGB:
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, texWidth, texHeight, 0, GL_RGBA,
GL_UNSIGNED_BYTE, addr imageData[0])