遊戲開發/渲染與遊戲引擎/OpenGL/繪製幾何體
這是將三角形的頂點資料傳遞給 OpenGL 的方法。
資料在一個數組中指定，每三個頂點表示一個新的三角形。在此格式中，需要按照連線的順序指定資料。
#include <gl\glew.h>
#include <MyGLWindow.h>
void MyGLWindow::initializeGL(){
GLfloat verts[] =
{
//1st Triangle
+0.0f, +1.0f, +0.0f, //Vertex 1
-1.0f, -1.0f, -0.5f, //Vertex 2
+1.0f, -1.0f, +0.5f, //Vertex 3
//2nd Triangle
+0.0f, -1.0f, +0.0f, //Vertex 1
-1.0f, +1.0f, -0.5f, //Vertex 2
+1.0f, +1.0f, +0.5f, //Vertex 3
};
GLuint myBufferID;
glGenBuffers(1, &myBufferID); //Generate an identifier for the buffer ID
glBindBuffer(GL_ARRAY_BUFFER, myBufferID); //Bind it to the array buffer binding point
glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts, GL_STATIC_DRAW); //Send the size of the data and the data to the buffer assigned to the array buffer binding point.
//Describing the data
glEnableVertexAttribArray(0); //The first attribute to send to openGL (later redirected through a vertex shader)
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0,0); //There are 3 floats per vertex...
}
void MyGLWindow::paintGL(){
glViewport(0, 0, width(), height()); //Fixes the resizing to change ratio of triangle
glDrawArrays(GL_TRIANGLES, 0, 6); //Connect the 6 vertices into triangles (triangle=3, 6/3 = 2 triangles)
}
這段程式碼很容易修改為只傳遞 2D 資料，為此你需要更改兩件事。
- 陣列應該只包含 X 和 Y 座標。
- glVertexAttribPointer 引數 2 需要從 3 更改為 2。
此程式的新版本傳遞頂點位置的 ID，以說明如何連線三角形。對於沒有連線的基本三角形，這比之前效率低，但是對於大多數形狀，三角形將共享頂點，這意味著你不需要指定 3 個數據（XYZ，如果新增顏色和光照法線則更多），只需要傳遞一個額外的短整型作為頂點索引。這樣可以節省記憶體，因為需要更少的資料，並且對於動畫幾何體，這意味著需要傳送到 OpenGL 及更遠端的資料副本更少。
#include <gl\glew.h>
#include <MyGLWindow.h>
void MyGLWindow::initializeGL(){
GLfloat verts[] =
{
//1st Triangle
+0.0f, +1.0f, +0.0f, //Vertex 1
-1.0f, -1.0f, -0.5f, //Vertex 2
+1.0f, -1.0f, +0.5f, //Vertex 3
//2nd Triangle
+0.0f, -1.0f, +0.0f, //Vertex 1
-1.0f, +1.0f, -0.5f, //Vertex 2
+1.0f, +1.0f, +0.5f, //Vertex 3
};
GLuint myBufferID;
glGenBuffers(1, &myBufferID); //Num buffers, BufferID
glBindBuffer(GL_ARRAY_BUFFER, myBufferID);
glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts, GL_STATIC_DRAW);
//Assigning the positions of the vertices into 2 triangle (triangle 1= {0,1,2}, triangle 2={3,4,5})
GLushort indices[] = {0,1,2, 3,4,5};
GLuint indexBufferID;
glGenBuffers(1, &indexBufferID); //Generate an identifier for the index buffer ID
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferID); //Link the index buffer to the element array buffer binding point
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW); //Send the size of the data and the data to the index buffer, linked to the element array buffer binding point.
//Describing the data
glEnableVertexAttribArray(0); //The first attribute
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0,0); A vertex consists of 3 floats
}
void MyGLWindow::paintGL(){
glViewport(0, 0, width(), height()); //Fixes the resizing to change ratio of triangle
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_SHORT, 0); //Notice this is different from above
}
注意：在設定片段著色器之前，顏色不會生效。但是，要設定片段著色器，你需要從頂點著色器傳送顏色資料。
#include <gl\glew.h>
#include <MyGLWindow.h>
void MyGLWindow::initializeGL(){
GLfloat verts[] =
{
//One colourful triangle being drawn
+0.0f, +1.0f, +0.0f, //Vertex 1
+1.0f, +0.0f, +0.0f, //Vertex 1's Color (Red)
-1.0f, -1.0f, -0.5f, //Vertex 2
+0.0f, +1.0f, +0.0f, //Vertex 2's Color (Green)
+1.0f, -1.0f, +0.5f, //Vertex 3
+0.0f, +0.0f, +1.0f, //Vertex 3's Color (Blue)
};
GLuint myBufferID;
glGenBuffers(1, &myBufferID); //Num buffers, BufferID
glBindBuffer(GL_ARRAY_BUFFER, myBufferID);
glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts, GL_STATIC_DRAW);
GLushort indices[] = {0,1,2};
GLuint indexBufferID;
glGenBuffers(1, &indexBufferID);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBufferID);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
//Describing the data
glEnableVertexAttribArray(0); //The first attribute (Vertex data)
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(float) *6,0); //There are 6 floats worth of data from the start of one list of vertices and the next set of vertices
glEnableVertexAttribArray(1); //The second attribute (Color data)
glVertexAttribPointer(1, 3, GL_FLOAT, GL_FALSE, sizeof(float) *6, (char*)(sizeof(float)*3)); //There are 6 floats worth of data from the start of one list of vertices and the next set of vertices. The first piece of data starts after 3 floats.
}
void MyGLWindow::paintGL(){
glViewport(0, 0, width(), height()); //Fixes the resizing to change ratio of triangle
glDrawElements(GL_TRIANGLES, 3, GL_UNSIGNED_SHORT, 0);
}