How to clip texture in OpenGL? - opengl

Question

I need to crop the image. But in opencv, it will create error because of integer domain. So I want to crop every single unit in float domain to reduce the offset error. Maybe openGL can help me, but I'm not good at it.
The image just like this ( but not this one ):
I want every black and white unit, then save them in cv::Mat.
I guess maybe shader or loop or something else can repeat to crop all block, then save them.
Now I can get one single unit. Like this:
glfwInit();//initalization
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(100, 100, "LearnOpenGL", nullptr, nullptr);
if (window == nullptr)
{
cout << "Failed to create GLFW window" << endl;
glfwTerminate();
return false;
}
glfwMakeContextCurrent(window);
if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
{
std::cout << "Failed to initialize GLAD" << std::endl;
return false;
}
Shader ourShader("vertex.vs.glsl", "fragment.fs.glsl");
float unitWidth = moduleLength / (float)tex.cols;
float startP_x = 100.0f / (float)tex.cols + unitWidth * 2;
float startP_y = 104.0f / (float)tex.rows + unitWidth * 2;
float vertices[] = {
// positions // texture coords (note that we changed them to 'zoom in' on our texture image)
0.5f, 0.5f, 0.0f, startP_x + unitWidth, startP_y, // top right
0.5f, -0.5f, 0.0f, startP_x + unitWidth, startP_y + unitWidth, // bottom right
-0.5f, -0.5f, 0.0f, startP_x, startP_y + unitWidth, // bottom left
-0.5f, 0.5f, 0.0f, startP_x, startP_y // top left
};
unsigned int indices[] = {
0, 1, 3, // first triangle
1, 2, 3 // second triangle
};
unsigned int VBO, VAO, EBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &VBO);
glGenBuffers(1, &EBO);
glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
// position attribute
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
// texture coord attribute
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(1);
// texture
// ---------
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
//// set the texture wrapping parameters
// set the texture wrapping parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_BORDER);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_BORDER);
// set texture filtering parameters
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
GLubyte* pixels;
int width = tex.cols;
int height = tex.rows;
int pixellength = width * height*tex.channels();
pixels = new GLubyte[pixellength];
memcpy(pixels, tex.data, pixellength * sizeof(unsigned char));
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, pixels);
free(pixels);
while (!glfwWindowShouldClose(window))
{
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// bind Texture
glBindTexture(GL_TEXTURE_2D, texture);
// draw our first triangle
ourShader.use();
// create transformations
glm::mat4 model = glm::mat4(1.0f); // make sure to initialize matrix to identity matrix first
glm::mat4 view = glm::mat4(1.0f);
glm::mat4 projection = glm::mat4(1.0f);
model = glm::rotate(model, glm::radians(0.0f), glm::vec3(1.0f, 0.0f, 0.0f));
view = glm::translate(view, glm::vec3(0.0f, 0.0f, -1.1f));
projection = glm::perspective(glm::radians(45.0f), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
// retrieve the matrix uniform locations
unsigned int modelLoc = glGetUniformLocation(ourShader.ID, "model");
unsigned int viewLoc = glGetUniformLocation(ourShader.ID, "view");
unsigned int transformLoc = glGetUniformLocation(ourShader.ID, "projection");
glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model));
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, &view[0][0]);
glUniformMatrix4fv(transformLoc, 1, GL_FALSE, glm::value_ptr(projection));
glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0); // set the count to 6 since we're drawing 6 vertices now (2 triangles); not 3!
glfwPollEvents();
glfwSwapBuffers(window);
}
glDeleteVertexArrays(1, &VAO);
glDeleteBuffers(1, &VBO);
glDeleteBuffers(1, &EBO);
glfwTerminate();
return true;
vetex shader:
#version 330 core
layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 aTexCoord;
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;
out vec2 TexCoord;
void main()
{
gl_Position = projection * view * model *vec4(aPos, 1.0);
TexCoord = vec2(aTexCoord.x, aTexCoord.y);
}
fragment shader:
#version 330 core
out vec4 FragColor;
in vec2 TexCoord;
uniform sampler2D texture1;
void main()
{
FragColor = texture(texture1, TexCoord);
}