如何使用多個 VAO 和 VBO 在 OpenGL 中繪制多個對象？

Question

我正在嘗試使用多個 VAO 和 VBO 在 OpenGL 中渲染多個對象。 要使用相同的頂點渲染多個對象，我已經完成了，但我想要做的是為每個對象使用不同的頂點，例如繪制一個正方形和一個圓形。 對於正方形，我只需要 6 個頂點，但對於圓形，我需要 360 個頂點。我在讀取或創建着色器時出錯。

這是頂點着色器：

#version 330 core

layout (location = 0) in vec4 position;

uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;

void main()
{
    gl_Position = projection * view * model * position;
}

片段着色器：

#version 330 core

layout(location = 0) out vec4 color;

uniform vec4 u_Color;

void main()
{
    color = u_Color;
}

VAO 和 VBO 生成和綁定

// Circle
std::vector<VertexFormat> vertices;

for (int i = 0; i < 360; i++)
{
    GLfloat angle = i * ((2.0f * 3.14159f) / 360);
    vertices.push_back(VertexFormat(glm::vec3(cos(angle) * 100.0f, sin(angle) * 100.0f, 0.0f)));
}

// Pipette object
std::vector<VertexFormat> pipetteVertices;
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 500.0f, 0.0f))); // 0
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 500.0f, 0.0f))); // 1
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 700.0f, 0.0f))); // 2
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 700.0f, 0.0f))); // 3
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 500.0f, 0.0f)));
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 700.0f, 0.0f)));

GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);

GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(VertexFormat) * 6, &pipetteVertices[0], GL_STATIC_DRAW);

//Position attribute
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VertexFormat), (GLvoid *)0);

GLuint vao2;
glGenVertexArrays(1, &vao2);
glBindVertexArray(vao2);

GLuint vbo2;
glGenBuffers(1, &vbo2);
glBindBuffer(GL_ARRAY_BUFFER, vbo2);
glBufferData(GL_ARRAY_BUFFER, sizeof(VertexFormat) * 360, &vertices[0], GL_STATIC_DRAW);

//Position attribute
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VertexFormat), (GLvoid *) 0);

glBindBuffer(GL_ARRAY_BUFFER, 0);

以及渲染循環中的繪制調用：

    //Get the uniform locations of model, view and projection matrices
    modelID = glGetUniformLocation(program, "model");
    viewID = glGetUniformLocation(program, "view");
    projectionID = glGetUniformLocation(program, "projection");

    //View transform
    glm::mat4 view = glm::lookAt(glm::vec3(0, 0, 2), glm::vec3(0, 0, 0), glm::vec3(0, 1, 0));
    //Projection transform
    //glm::mat4 projection = glm::perspective(45.0f, (GLfloat)screenWidth / (GLfloat)screenHeight, 0.1f, 1000.0f);
    glm::mat4 projection = glm::ortho(0.0f, (GLfloat)screenWidth, 0.0f,  (GLfloat)screenHeight, 0.1f, 10.0f);

    {
        glUniformMatrix4fv(viewID, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projectionID, 1, GL_FALSE, glm::value_ptr(projection));

        glm::mat4 translate = glm::translate(glm::mat4(1.0), glm::vec3(100.0f + move_x, 100.0f + move_y, 0.0f));
        glm::mat4 rotate = glm::rotate(glm::mat4(1.0), 0.0f, glm::vec3(0.0f, 0.0f, 1.0f));
        glm::mat4 scale = glm::scale(glm::mat4(1.0), glm::vec3(1.0f, 1.0f, 2.0f));

        glm::mat4 model = translate * rotate * scale;
        glUniformMatrix4fv(modelID, 1, GL_FALSE, glm::value_ptr(model));

        glUniform4f(color, 0.0f, 0.0f, 1.0f, 1.0f);

        //Render
        glDrawArrays(GL_TRIANGLE_FAN, 0, 360);
    }

    {
        glUniformMatrix4fv(viewID, 1, GL_FALSE, glm::value_ptr(view));
        glUniformMatrix4fv(projectionID, 1, GL_FALSE, glm::value_ptr(projection));

        glm::mat4 translate = glm::translate(glm::mat4(1.0), glm::vec3(300.0f + injPipette.x, 300.0f + injPipette.y, 0.0f));
        glm::mat4 rotate = glm::rotate(glm::mat4(1.0), 0.0f, glm::vec3(0.0f, 0.0f, 1.0f));
        glm::mat4 scale = glm::scale(glm::mat4(1.0), glm::vec3(1.0f, 1.0f, 2.0f));

        glm::mat4 model = translate * rotate * scale;
        glUniformMatrix4fv(modelID, 1, GL_FALSE, glm::value_ptr(model));

        glUniform4f(color, 1.0f, 0.0f, 0.0f, 0.5f);

        //Render
        glDrawArrays(GL_TRIANGLES, 0, 6);
    }

我重復一遍，使用我已經完成的相同頂點繪制多個對象。 我需要知道如何使用相同的頂點和片段着色器但不同數量的頂點來繪制多個對象。 該項目很小，僅在 2D 中渲染最多 10 個對象。

Answer 1

glDrawArrays等繪圖命令處理和繪制當前綁定的Vertex Array Object 中指定的通用頂點屬性數據數組。

這意味着您需要在執行 Draw 調用之前綁定正確的頂點數組對象：

// [...]

glBindVertexArray(vao2);
glDrawArrays(GL_TRIANGLE_FAN, 0, 360);

// [...]

glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLES, 0, 6); 

Answer 2

@Kenny83 自從我接觸OpenGL已經有一段時間了，老實說我不記得我從哪里得到VertexFormat但幸運的是我找到了帶有代碼的項目。 我不知道如何在評論中添加片段，我認為這甚至不可能，所以我將其添加為答案：

#pragma once
#include "glm\glm.hpp"

struct VertexFormat
{

    glm::vec3 position;

    VertexFormat(const glm::vec3 &iPos)
    {
        position = iPos;
    }

    VertexFormat()
    {

    }

};

希望能幫助到你。