1
我想用着色器使用OpenGL在我的屏幕上呈現兩個三角形;一個大紅色，一個小藍色。每個三角形由一組頂點位置和顏色以及一組頂點索引定義。我爲每個三角形使用不同的頂點數組對象。使用OpenGL和頂點數組對象呈現兩個對象
下面是我的代碼，我已經減少到最小的可編譯的例子，它仍然給我的問題。問題是隻有第二個三角形（object2，小的藍色三角形）被渲染。所以，即使我綁定第一個三角形（object1，大紅色三角形）的頂點數組對象，然後繪製元素，但不會呈現此對象。
我在做什麼錯？
#include <GL/glew.h>
#include <GL/glut.h>
#include <Eigen/Eigen>
#include <fstream>
GLuint object1_vertex_buffer, object1_colour_buffer, object1_index_buffer, object1_vertex_array;
GLuint object2_vertex_buffer, object2_colour_buffer, object2_index_buffer, object2_vertex_array;
GLuint shader_program, vertex_shader, fragment_shader;
void RenderScene()
{
glClear(GL_COLOR_BUFFER_BIT);
glClear(GL_DEPTH_BUFFER_BIT);
glBindVertexArray(object1_vertex_array);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, (void*)0);
glBindVertexArray(object2_vertex_array);
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_INT, (void*)0);
glutSwapBuffers();
}
int main(int argc, char** argv)
{
// Make the objects
Eigen::Vector3f object1_vertices[3];
object1_vertices[0] << 0, 0, 0;
object1_vertices[1] << 0.8, 0, 0;
object1_vertices[2] << 0.8, 0.8, 0;
Eigen::Vector3f object1_colours[3];
object1_colours[0] << 1.0, 0.0, 0.0;
object1_colours[1] << 1.0, 0.0, 0.0;
object1_colours[2] << 1.0, 0.0, 0.0;
int object1_indices[3];
object1_indices[0] = 0;
object1_indices[1] = 1;
object1_indices[2] = 2;
Eigen::Vector3f object2_vertices[3];
object2_vertices[0] << 0, 0, 0;
object2_vertices[1] << 0.5, 0, 0;
object2_vertices[2] << 0.5, 0.5, 0;
Eigen::Vector3f object2_colours[3];
object2_colours[0] << 0.0, 0.0, 1.0;
object2_colours[1] << 0.0, 0.0, 1.0;
object2_colours[2] << 0.0, 0.0, 1.0;
int object2_indices[3];
object2_indices[0] = 0;
object2_indices[1] = 1;
object2_indices[2] = 2;
// Set up OpenGL
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowSize(1000, 1000);
glutCreateWindow("Test");
glutDisplayFunc(RenderScene);
glewInit();
glClearColor(1.0f, 1.0f, 1.0f, 0.0f);
glEnable(GL_DEPTH_TEST);
// Make the buffers
glGenBuffers(1, &object1_vertex_buffer);
glGenBuffers(1, &object1_colour_buffer);
glGenBuffers(1, &object1_index_buffer);
glGenVertexArrays(1, &object1_vertex_array);
glGenBuffers(1, &object2_vertex_buffer);
glGenBuffers(1, &object2_colour_buffer);
glGenBuffers(1, &object2_index_buffer);
glGenVertexArrays(1, &object2_vertex_array);
// Fill the buffer data
glBindVertexArray(object1_vertex_array);
glBindBuffer(GL_ARRAY_BUFFER, object1_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(object1_vertices), &object1_vertices[0], GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, object1_colour_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(object1_colours), &object1_colours[0], GL_STATIC_DRAW);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object1_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 3 * sizeof(int), &object1_indices[0], GL_STATIC_DRAW);
glBindVertexArray(object2_vertex_array);
glBindBuffer(GL_ARRAY_BUFFER, object2_vertex_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(object2_vertices), &object2_vertices[0], GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, object2_colour_buffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(object2_colours), &object2_colours[0], GL_STATIC_DRAW);
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, object2_index_buffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 3 * sizeof(int), &object2_indices[0], GL_STATIC_DRAW);
// Make the shader program
shader_program = glCreateProgram();
vertex_shader = glCreateShader(GL_VERTEX_SHADER);
std::ifstream vertex_file_in;
vertex_file_in.open("../src/vertex-shader.glsl");
std::stringstream vertex_file_stream;
vertex_file_stream << vertex_file_in.rdbuf();
std::string vertex_shader_string = vertex_file_stream.str();
std::cout << vertex_shader_string << std::endl;
const GLchar* ptr_vertex_shader_string = &vertex_shader_string[0];
const GLchar** vertex_shader_strings = &ptr_vertex_shader_string;
int vertex_shader_lengths[] = {(int)vertex_shader_string.length()};
glShaderSource(vertex_shader, 1, vertex_shader_strings, vertex_shader_lengths);
glCompileShader(vertex_shader);
glAttachShader(shader_program, vertex_shader);
fragment_shader = glCreateShader(GL_FRAGMENT_SHADER);
std::ifstream fragment_file_in;
fragment_file_in.open("../src/fragment-shader.glsl");
std::stringstream fragment_file_stream;
fragment_file_stream << fragment_file_in.rdbuf();
std::string fragment_shader_string = fragment_file_stream.str();
const GLchar* ptr_fragment_shader_string = &fragment_shader_string[0];
const GLchar** fragment_shader_strings = &ptr_fragment_shader_string;
int fragment_shader_lengths[] = {(int)fragment_shader_string.length()};
glShaderSource(fragment_shader, 1, fragment_shader_strings, fragment_shader_lengths);
glCompileShader(fragment_shader);
glAttachShader(shader_program, fragment_shader);
glBindAttribLocation(shader_program, 0, "position");
glBindAttribLocation(shader_program, 1, "colour");
glLinkProgram(shader_program);
glUseProgram(shader_program);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
// Run the main loop
glutMainLoop();
}
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// Vertex shader
#version 330
layout (location = 0) in vec3 position;
layout (location = 1) in vec3 colour;
out vec4 frag_colour;
void main()
{
gl_Position = vec4(position, 1.0);
frag_colour = vec4(colour, 1.0);
}
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// Fragment shader
#version 330
in vec4 frag_colour;
void main()
{
gl_FragColor = frag_colour;
}