How to Make Draw an Equilateral Traingle Opengl

How to draw multiple triangle in OpenGL C++?

Lucas Huang

I was able to get to draw a single object with an array of vertices. However, it gave me a hard time when it comes to draw multiple objects.

I have an array of data like this and three vertices render one triangle:

                  -0.0570917f,0.490469f,-0.142433f -0.0581126f,0.5f,-0.160615f -0.0651903f,0.490827f,-0.147409f -0.0501295f,0.499886f,-0.158146f -0.0491703f,0.49039f,-0.140236f -0.0422027f,0.499864f,-0.157942f -0.041255f,0.49031f,-0.138206f -0.0333885f,0.490314f,-0.137995f -0.0967512f,0.48302f,-0.150394f ...                                  

And I am trying to render multiple triangles with the following code:

                  // this array contains arrays with one vertex (three elements) vector<vector<GLfloat>> pointVertex;  // Render OpenGL here for (int i = 0; i < pointVertex.size(); i++) {     vector<GLfloat> temp = pointVertex[i];     GLfloat *pointVertexArrayPoint = temp.data();     glEnable(GL_POINT_SMOOTH);     glEnableClientState(GL_VERTEX_ARRAY);     glVertexPointer(3, GL_FLOAT, 0, pointVertexArrayPoint);     glDrawArrays(GL_LINES, 0, temp.size());     glDisableClientState(GL_VERTEX_ARRAY);     glDisable(GL_POINT_SMOOTH); }                                  

Now, I am getting a result but it all starts at the same point. I want it to render different multiple separate triangles. How can I change it?

Brandon

There's a few ways to do this without straying away from the technique you are using (Legacy pipeline)..

The below code will draw two triangles.. like so:

Each triangle is rendered with 1 draw call per triangle:

                  void onDisplayRefreshSO(void* ctx) {     //Setup OpenGL once..     static std::once_flag flag;     std::call_once(flag, []{         GLfloat view_port[4] = {0};         glGetFloatv(GL_VIEWPORT, &view_port[0]);         GLfloat screen_width = view_port[2] - view_port[0];         GLfloat screen_height = view_port[3] - view_port[1];          glMatrixMode(GL_PROJECTION);         gluPerspective(45.0, screen_width / screen_height, 0.1f, 1000.0f);          glMatrixMode(GL_MODELVIEW);         glLoadIdentity();          glShadeModel(GL_SMOOTH);                            // Enable Smooth Shading         glClearDepth(1.0f);                                    // Depth Buffer Setup         glEnable(GL_DEPTH_TEST);                            // Enables Depth Testing         glDepthFunc(GL_LEQUAL);                                // The Type Of Depth Testing To Do         glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);    // Really Nice Perspective Calculations     });        /** Setup Drawing Triangles **/     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);     glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);       GLfloat normals[] = {         0, 0, 1,   0, 0, 1,   0, 0, 1,         0, 0, 1,   0, 0, 1,   0, 0, 1     };      GLfloat colors[] = {         1, 1, 1,   1, 1, 0,   1, 0, 0,         0, 1, 1,   0, 1, 0,   0, 0, 1     };      GLfloat vertices[] = {         1, 1, 1,  -1, 1, 1,  -1,-1, 1,         1, 1, 1,  1, -1, 1,  -1,-1, 1     };        //9 floats per triangle.. 3 * (X, Y, Z)..     for (int i = 0; i < sizeof(vertices) / sizeof(vertices[0]) / 9; ++i)     {         glEnableClientState(GL_NORMAL_ARRAY);         glEnableClientState(GL_COLOR_ARRAY);         glEnableClientState(GL_VERTEX_ARRAY);         glNormalPointer(GL_FLOAT, 0, normals + (i * 9));         glColorPointer(3, GL_FLOAT, 0, colors + (i * 9));         glVertexPointer(3, GL_FLOAT, 0, vertices + (i * 9));          glPushMatrix();         glTranslatef(-1.0f, 0.0f, -6.0f);         glDrawArrays(GL_TRIANGLES, 0, 3); //3 vertices (X, Y, Z) per triangle..         glPopMatrix();          glDisableClientState(GL_VERTEX_ARRAY);         glDisableClientState(GL_COLOR_ARRAY);         glDisableClientState(GL_NORMAL_ARRAY);     } }                                  

All triangles rendered in a single draw call:

                  void onDisplayRefreshSO2(void* ctx) {     //Setup OpenGL once..     static std::once_flag flag;     std::call_once(flag, []{         GLfloat view_port[4] = {0};         glGetFloatv(GL_VIEWPORT, &view_port[0]);         GLfloat screen_width = view_port[2] - view_port[0];         GLfloat screen_height = view_port[3] - view_port[1];          glMatrixMode(GL_PROJECTION);         gluPerspective(45.0, screen_width / screen_height, 0.1f, 1000.0f);          glMatrixMode(GL_MODELVIEW);         glLoadIdentity();          glShadeModel(GL_SMOOTH);                            // Enable Smooth Shading         glClearDepth(1.0f);                                    // Depth Buffer Setup         glEnable(GL_DEPTH_TEST);                            // Enables Depth Testing         glDepthFunc(GL_LEQUAL);                                // The Type Of Depth Testing To Do         glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);    // Really Nice Perspective Calculations     });       glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);     glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);       /** Setup Drawing Triangles **/     GLfloat normals[] = {         0, 0, 1,   0, 0, 1,   0, 0, 1,         0, 0, 1,   0, 0, 1,   0, 0, 1     };      GLfloat colors[] = {         1, 1, 1,   1, 1, 0,   1, 0, 0,         0, 1, 1,   0, 1, 0,   0, 0, 1     };      GLfloat vertices[] = {         1, 1, 1,  -1, 1, 1,  -1,-1, 1,         1, 1, 1,  1, -1, 1,  -1,-1, 1     };       //Draw both triangles in a single call..     glEnableClientState(GL_NORMAL_ARRAY);     glEnableClientState(GL_COLOR_ARRAY);     glEnableClientState(GL_VERTEX_ARRAY);     glNormalPointer(GL_FLOAT, 0, normals);     glColorPointer(3, GL_FLOAT, 0, colors);     glVertexPointer(3, GL_FLOAT, 0, vertices);      glPushMatrix();     glTranslatef(-1.0f, 0.0f, -6.0f);     glDrawArrays(GL_TRIANGLES, 0, (sizeof(vertices) / sizeof(vertices[0])) / 3); //6 vertices (X, Y, Z) for 2 triangles..     glPopMatrix();      glDisableClientState(GL_VERTEX_ARRAY);     glDisableClientState(GL_COLOR_ARRAY);     glDisableClientState(GL_NORMAL_ARRAY); }                                  

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edited at 2021-04-27

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How to Make Draw an Equilateral Traingle Opengl

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