[英]OpenGL C++ order for using a vertex buffer and a texture buffer
我在將紋理加載到三角帶上時遇到問題。 我遵循的是Anton Gerdelan的教程 ,在主程序失敗之后,我回到了基礎知識,只是試圖制作一個普通的正方形並將其紋理放在上面(骷髏和交叉骨)。
我完全從他的“ Hello Triangle”頁面復制並粘貼了代碼,該頁面可以正常工作,但是一旦嘗試使其適合他上面的紋理教程中的代碼(並將三角形更改為正方形),我得到的就是一個帶有白色大正方形沒有質感。
我已經使用glGetShaderiv()檢查了着色器的狀態,並且它們返回正值,我檢查了加載的圖像以查看像素數據是否合理,因此我認為我的錯誤在於聲明我的VBO或其中的順序/參數我正在使用它們。
這是我復制的完整代碼,可以在Visual Studio 2013中很好地編譯,只是輸出不是預期的。
我正在使用GLEW和GLFW的靜態庫以及STBI Image標頭
#include <GL/glew.h> // include GLEW and new version of GL on Windows
#include <GL/glfw3.h> // GLFW helper library
#include <stdio.h>
#define STB_IMAGE_IMPLEMENTATION
#include <stb/stb_image.h>
const char* vertex_shader =
"#version 400\n"
"in vec3 vp;"
"layout (location=1) in vec2 vt; // per-vertex texture co-ords"
"out vec2 texture_coordinates; "
"void main () {"
" gl_Position = vec4 (vp, 1.0);"
" texture_coordinates = vt; "
"}";
const char* fragment_shader =
"#version 400\n"
"in vec2 texture_coordinates;"
"uniform sampler2D basic_texture;"
"out vec4 frag_colour;"
"void main () {"
"vec4 texel = texture(basic_texture, texture_coordinates);"
"frag_colour = texel; "
"}";
float points[] = {
-0.5f, -0.5f, 0.0f,
-0.5f, 0.5f, 0.0f,
0.5f, -0.5f, 0.0f,
0.5f, 0.5f, 0.0f
};
float texcoords[] = {
0.0f, 1.0f,
0.0f, 0.0f,
1.0, 0.0,
1.0, 0.0,
1.0, 1.0,
0.0, 1.0
};
GLFWwindow* window;
unsigned int vt_vbo;
unsigned int tex = 0;
GLuint vao = 0;
GLuint vbo = 0;
GLuint shader_programme;
void initializeGL(){
// start GL context and O/S window using the GLFW helper library
if (!glfwInit()) {
printf("ERROR: could not start GLFW3\n");
return;
}
window = glfwCreateWindow(640, 480, "Texture Test", NULL, NULL);
if (!window) {
printf("ERROR: could not open window with GLFW3\n");
glfwTerminate();
return;
}
glfwMakeContextCurrent(window);
// start GLEW extension handler
glewExperimental = GL_TRUE;
glewInit();
// get version info
const GLubyte* renderer = glGetString(GL_RENDERER); // get renderer string
const GLubyte* version = glGetString(GL_VERSION); // version as a string
printf("Renderer: %s\n", renderer);
printf("OpenGL version supported %s\n", version);
// tell GL to only draw onto a pixel if the shape is closer to the viewer
glEnable(GL_DEPTH_TEST); // enable depth-testing
glDepthFunc(GL_LESS); // depth-testing interprets a smaller value as "closer"
}
void startShaders(){
GLuint vs = glCreateShader(GL_VERTEX_SHADER);
glShaderSource(vs, 1, &vertex_shader, NULL);
glCompileShader(vs);
GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
glShaderSource(fs, 1, &fragment_shader, NULL);
glCompileShader(fs);
shader_programme = glCreateProgram();
glAttachShader(shader_programme, fs);
glAttachShader(shader_programme, vs);
glLinkProgram(shader_programme);
GLint vsstat;
glGetShaderiv(vs, GL_COMPILE_STATUS, &vsstat);
GLint fsstat;
glGetShaderiv(fs, GL_COMPILE_STATUS, &fsstat);
printf("%i\n%i\n", vsstat, fsstat);
}
void loadImage(){
int x, y, n;
int force_channels = 4;
unsigned char* image_data = stbi_load("skulluvmap.png", &x, &y, &n, force_channels);
if (!image_data) {
printf("ERROR: could not load %s\n", "skulluvmap.png");
}
int width_in_bytes = x * 4;
unsigned char *top = NULL;
unsigned char *bottom = NULL;
unsigned char temp = 0;
int half_height = y / 2;
for (int row = 0; row < half_height; row++) {
top = image_data + row * width_in_bytes;
bottom = image_data + (y - row - 1) * width_in_bytes;
for (int col = 0; col < width_in_bytes; col++) {
temp = *top;
*top = *bottom;
*bottom = temp;
top++;
bottom++;
}
}
printf("first 4 bytes are: %i %i %i %i\n",
image_data[0], image_data[1], image_data[2], image_data[3]
);
glGenTextures(1, &tex);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, tex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, x, y, 0, GL_RGBA, GL_UNSIGNED_BYTE, image_data);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
}
void generateBuffers(){
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(float), points, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);
glEnableVertexAttribArray(0); // don't forget this!
glGenBuffers(1, &vt_vbo);
glBindBuffer(GL_ARRAY_BUFFER, vt_vbo);
glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(float), texcoords, GL_STATIC_DRAW);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, NULL);
glEnableVertexAttribArray(1); // don't forget this!
}
void mainLoop(){
while (!glfwWindowShouldClose(window)) {
// wipe the drawing surface clear
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
int tex_loc = glGetUniformLocation(shader_programme, "basic_texture");
glUseProgram(shader_programme);
glUniform1i(tex_loc, 0); // use active texture 0
// draw points 0-4 from the currently bound VAO with current in-use shader
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// update other events like input handling
glfwPollEvents();
// put the stuff we've been drawing onto the display
glfwSwapBuffers(window);
}
}
int main() {
initializeGL();
startShaders();
loadImage();
generateBuffers();
mainLoop();
// close GL context and any other GLFW resources
glfwTerminate();
return 0;
}
您正在濫用第二個緩沖區,該緩沖區應該是texcoords
的緩沖區。 因此,您真正想要實現的是每個頂點都有一對紋理坐標。 這意味着您的texcoords數組實際上應該存儲4對,因為您在points數組中有4個三元組。 所以這是第一個解決方法。 您可能希望它看起來像:
float texcoords[] = {
0.0f, 1.0f,
0.0f, 0.0f,
1.0, 0.0,
1.0, 1.0,
};
然后在generateBuffers
,您的vt_vbo
是錯誤的。 數據應通過以下方式傳遞:
glBufferData(GL_ARRAY_BUFFER, 8 * sizeof(float), texcoords, GL_STATIC_DRAW);
因為您只想在那里傳遞8個值。 每個頂點2個texcoords。
編輯:
但是,這並不能完全解釋為什么紋理根本不出現。 我最初以為您的texcoords
指針可能有問題,但事實並非如此。
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