Original post:
https://computergraphics.stackexchange.com/questions/4793/how-can-i-generate-mipmaps-manually
It was a silly mistake, I forgot to set all texture coordinates :P
OpenGL is fairly difficult to learn. According to my understanding of mipmaps, I can set each mipmap level manually, so I could change the image to use when my texture looks greater or smaller.
I tried the following code but doesn't matter the size of the triangle, it always take the first mipmap level. Why? if the triangle is closer to any other mipmap level, why does not take it?
I really hate putting a bunch of code in my questions because I force others to waste time analyzing the code instead of putting the most revelant snippet code, but I don't know where is the problem and I have not alternative. Sorry :(
#include <iostream>
#define GLEW_STATIC
#include <GL/glew.h>
#include <GLFW/glfw3.h>
const GLchar* VERTEX_SHADER_SOURCE =
"#version 330 core \n"
"layout (location = 0) in vec2 position; \n"
"layout (location = 1) in vec2 myTexCoord; \n"
" \n"
"out vec2 TexCoord; \n"
" \n"
"void main() \n"
"{ \n"
" gl_Position = vec4(position,0.0f, 1.0f);\n"
" TexCoord = myTexCoord; \n"
"} \n";
const GLchar* FRAGMENT_SHADER_SOURCE =
"#version 330 core \n"
"in vec2 TexCoord; \n"
" \n"
"out vec4 color; \n"
" \n"
"uniform sampler2D ourTexture; \n"
" \n"
"void main() \n"
"{ \n"
" color = texture(ourTexture, TexCoord);\n"
"} \n";
int main()
{
//Change the value of size by 1,2,4,8,16,32,64,128 or 256 and see how the color of the triangle doesn't change. Why does it happen?
GLint size = 128;
//INIT STUFFS
glfwInit();
glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
GLFWwindow* window = glfwCreateWindow(size,size, "", nullptr, nullptr);
glfwMakeContextCurrent(window);
glewExperimental = GL_TRUE;
glewInit();
glViewport(0, 0,size,size);
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
//Our image for the mipmap with odd level and green color
//The dimensions are 256 x 256 and is multiplied by 3 because I defined R,G and B colors
unsigned char imageArray[256*256*3];
for(int i = 0; i < 256*256*3; i++){
if((i+2)%3 == 0)
imageArray[i] = 255;
else
imageArray[i] = 0;
}
//Our image for the mipmap with pair level and red color
unsigned char imageArray2[256*256*3];
for(int i = 0; i < 256*256*3; i++){
if(i%3 == 0)
imageArray2[i] = 255;
else
imageArray2[i] = 0;
}
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL, 8);
//All mipmap levels defined by hand
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, 256, 256, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
glTexImage2D(GL_TEXTURE_2D, 1, GL_RGB, 128, 128, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
glTexImage2D(GL_TEXTURE_2D, 2, GL_RGB, 64, 64, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
glTexImage2D(GL_TEXTURE_2D, 3, GL_RGB, 32, 32, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
glTexImage2D(GL_TEXTURE_2D, 4, GL_RGB, 16, 16, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
glTexImage2D(GL_TEXTURE_2D, 5, GL_RGB, 8, 8, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
glTexImage2D(GL_TEXTURE_2D, 6, GL_RGB, 4, 4, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
glTexImage2D(GL_TEXTURE_2D, 7, GL_RGB, 2, 2, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray2);
glTexImage2D(GL_TEXTURE_2D, 8, GL_RGB, 1, 1, 0, GL_RGB, GL_UNSIGNED_BYTE, imageArray);
GLfloat vertices[] = {
-1.0f, -1.0f, 1.0f, -1.0f, 0.0f, 1.0f, //vertex coordinates
0.0f, 0.0f //Triangle's texture coordinates
};
//VAOs AND VBOs
GLuint VAO, VBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid*)0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(GLfloat), (GLvoid*)(sizeof(GLfloat)*3*2));
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
//SHADERS
GLuint program;
GLuint vertex, fragment;
vertex = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vertex, 1, &VERTEX_SHADER_SOURCE, NULL);
glCompileShader(vertex);
fragment = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fragment, 1, &FRAGMENT_SHADER_SOURCE, NULL);
glCompileShader(fragment);
program = glCreateProgram();
glAttachShader(program, vertex);
glAttachShader(program, fragment);
glLinkProgram(program);
glDeleteShader(vertex);
glDeleteShader(fragment);
glUseProgram(program);
//DRAWING OUR TRIANGLE
glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_TRIANGLES, 0,3);
glfwSwapBuffers(window);
while (!glfwWindowShouldClose(window))
glfwPollEvents();
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glfwTerminate();
return 0;
}
