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john_b
05-27-2017, 05:20 PM
Hi,
my program uses one VAO, 2 VBOs and 2 EBOs. The program draws from the VBO very oddly
This is how the program should function:


//cube
GLfloat vertices1[] = {
0.5f, 0.5f, 0.5f,
0.5f, 0.5f, -0.5f,
0.5f, -0.5f, 0.5f,
0.5f, -0.5f, -0.5f,
-0.5f, 0.5f, 0.5f,
-0.5f, 0.5f, -0.5f,
-0.5f, -0.5f, 0.5f,
-0.5f, -0.5f, -0.5f,

};
GLint indices1[]{
2, 0, 4,
4, 6, 2,
0, 2, 3,
3, 1, 0,
5, 1, 3,
3, 7, 5,
0, 1, 5,
4, 0, 5,
6, 4, 7,
4, 5, 7,
7, 3, 2,
7, 2, 6,
};

//loaded model
std::vector<GLfloat> teddy_vertices;
std::vector<GLuint> teddy_indices;
loadOBJ("teddy.obj", teddy_vertices, teddy_indices);


GLuint VAO, TEDDY, TEDDY_EBO, newVBO, newEBO;
glGenVertexArrays(1, &VAO);
glGenBuffers(1, &TEDDY);
glGenBuffers(1, &TEDDY_EBO);
glGenBuffers(1, &newVBO);
glGenBuffers(1, &newEBO);

glBindVertexArray(VAO);
glBindBuffer(GL_ARRAY_BUFFER, newVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, newEBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices1), indices1, GL_STATIC_DRAW);

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

glBindBuffer(GL_ARRAY_BUFFER, TEDDY);
glBufferData(GL_ARRAY_BUFFER, teddy_vertices.size()*sizeof(GLfloat), &teddy_vertices.front(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, TEDDY_EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, teddy_indices.size() * sizeof(GLuint), &teddy_indices.front(), GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, 0); // Note that this is allowed, the call to glVertexAttribPointer registered VBO as the currently bound vertex buffer object so afterwards we can safely unbind

glBindVertexArray(0);

//...

while (!glfwWindowShouldClose(window))
{
glfwPollEvents();

glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glm::mat4 model_matrix = glm::mat4(1.0f);
glm::mat4 view;
glm::mat4 tilt_view;
glm::mat4 projection;

view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp);//cameraPos + cameraFront

projection = glm::perspective(fov, (GLfloat)WIDTH / (GLfloat)HEIGHT, 0.1f, 100.0f);


glUniformMatrix4fv(modelLoc, 1, GL_FALSE, glm::value_ptr(model_matrix));
glUniformMatrix4fv(viewLoc, 1, GL_FALSE, glm::value_ptr(view));
glUniformMatrix4fv(projLoc, 1, GL_FALSE, glm::value_ptr(projection));
glUniform4fv(color, 1, glm::value_ptr(glm::vec4(1, 1, 1, 1)));

glBindVertexArray(VAO);

if (!teddy_render){
glBindBuffer(GL_ARRAY_BUFFER, TEDDY);
glDrawElements(
GL_TRIANGLES,
teddy_indices.size(),
GL_UNSIGNED_INT,
(void*)0
);
glBindBuffer(GL_ARRAY_BUFFER, 0);

}
else{
glBindBuffer(GL_ARRAY_BUFFER, newVBO);
glDrawElements(
GL_TRIANGLES,
36,
GL_UNSIGNED_INT, 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
glBindVertexArray(0);

glfwSwapBuffers(window);
}

glfwTerminate();
return 0;
}



this code only draws the loaded object incorrectly, and does not draw from the other VBO when wanted.

If in the game loop the code is changed to :


glBindVertexArray(VAO);

//if (!teddy_render){
glBindBuffer(GL_ARRAY_BUFFER, TEDDY);
glDrawElements(
GL_TRIANGLES,
teddy_indices.size(),
GL_UNSIGNED_INT,
(void*)0
);
glBindBuffer(GL_ARRAY_BUFFER, 0);

//}
//else{
// glBindBuffer(GL_ARRAY_BUFFER, newVBO);
// glDrawElements(
// GL_TRIANGLES,
// 36,
// GL_UNSIGNED_INT, 0);
// glBindBuffer(GL_ARRAY_BUFFER, 0);
//}


then the loaded object renders. Then if in the configuration above the game loop the cube is configured after the object, the cube renders even though the loaded object is being bound in the game loop with the cube code still commented out:



glBindVertexArray(VAO);

glBindBuffer(GL_ARRAY_BUFFER, TEDDY);
glBufferData(GL_ARRAY_BUFFER, teddy_vertices.size()*sizeof(GLfloat), &teddy_vertices.front(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, TEDDY_EBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, teddy_indices.size() * sizeof(GLuint), &teddy_indices.front(), GL_STATIC_DRAW);

glBindBuffer(GL_ARRAY_BUFFER, newVBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices1), vertices1, GL_STATIC_DRAW);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, newEBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices1), indices1, GL_STATIC_DRAW);

glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
glEnableVertexAttribArray(0);


glBindBuffer(GL_ARRAY_BUFFER, 0);

glBindVertexArray(0);


Thank you.

Dark Photon
05-28-2017, 08:19 PM
You need to read up on Vertex Array Objects (https://www.khronos.org/opengl/wiki/Vertex_Specification#Vertex_Array_Object) (VAOs). You're apparently misunderstanding how they work.

In particular, read up here about what happens to VAO state when you call glVertexAttribPointer.

Hint: You only have 1 VAO in your code snippet, so...