Barricadexx Barricadexx - 5 months ago 23
Linux Question

openGL on raspberry pi, indexed vertices

I'm trying to learn some basic opengl on raspberry pi.
I folow these tutorials
https://solarianprogrammer.com/2013/05/13/opengl-101-drawing-primitives/
http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-9-vbo-indexing/

I bumped in to a prbolem I can't solve.
I succesfully made it draw a triangle by listing vertices in an array, then I tried to do the same but using indexes, it doesn't work and I don't know why. it compiles succesfully and runs, but it doesn't display the triangle.

both tutorials make it so simple, add a buffer and replace "glDrawArrays" with "glDrawElements". but I must have missed something..

#include <stdio.h>
#include <unistd.h>
#include "../common/startScreen.h"
#include "../common/LoadShaders.h"

// Include GLM
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

using namespace glm;

int main(int argc, const char **argv)
{
float r=0.0;
InitGraphics();
printf("Screen started\n");
// Create and compile our GLSL program from the shaders
GLuint programID = LoadShaders( "simpletransformvertshader.glsl", "simplefragshader.glsl" );
printf("Shaders loaded\n");

// Get a handle for our "MVP" uniform
GLuint MatrixID = glGetUniformLocation(programID, "MVP");

// Get a handle for our buffers
GLuint vertexPosition_modelspaceID = glGetAttribLocation(programID, "vertexPosition_modelspace");

// Projection matrix
glm::mat4 Projection = glm::perspective(45.0f, 16.0f / 9.0f, 0.1f, 100.0f);



// Camera matrix
glm::mat4 View = glm::lookAt(
glm::vec3(0,0,5),
glm::vec3(0,0,0),
glm::vec3(0,1,0),
);

//glm::mat4 myMatrix = glm::translate(10.0f, 0.0f, 0.0f);

// Model matrix : an identity matrix (model will be at the origin)
glm::mat4 Model = glm::mat4(1.0f);
// Our ModelViewProjection : multiplication of our 3 matrices
glm::mat4 MVP = Projection * View * Model; // Remember, matrix$

//glm:mat4 MVP = Prpkection * View * Model;

GLfloat g_vertex_buffer_data[] = {
-1.0f, -1.0f, 0.0f,
1.0f, -1.0f, 0.0f,
1.0f, 1.0f, 0.0f,
// -1.0, 1.0f, 0.0f,
};



GLuint indices[3] = {
0,1,2,
// 2,3,0
};



// Set the viewport

GLuint vertexbuffer;
glGenBuffers(1, &vertexbuffer);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);
glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_bu$


GLuint eab;
glGenBuffers(1, &eab);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, eab);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STAT$



do{
// Model = glm::rotate(Model, r, glm::vec3(0.0f, 0.0f, 1.0f));

glClear( GL_COLOR_BUFFER_BIT );

// Use our shader
glUseProgram(programID);

// Send our transformation to the currently bound shader,
// in the "MVP" uniform
glUniformMatrix4fv(MatrixID, 1, GL_FALSE, &MVP[0][0]);

// 1rst attribute buffer : vertices
glEnableVertexAttribArray(vertexPosition_modelspaceID);
glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer);


glVertexAttribPointer(
vertexPosition_modelspaceID,

3, // size
GL_FLOAT, // type
GL_FALSE, // normalized?
0, // stride
(void*)0 // array buffer offset
);

// see above glEnableVertexAttribArray(vertexPosition_modelspaceID);

// Draw the triangle !
// glDrawArrays(GL_TRIANGLES, 0, 3);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, eab);
glDrawElements( GL_TRIANGLES, 3, GL_UNSIGNED_INT, 0);




glDisableVertexAttribArray(vertexPosition_modelspaceID);

updateScreen();
}
while(1);

// Cleanup VBO
glDeleteBuffers(1, &vertexbuffer);
glDeleteBuffers(1, &eab);
glDeleteProgram(programID);


}

Answer

GLES 1.x/2.x does not support 32 bit indices by default. You can use at most 16 bit indices, so you should change your code to:

GLushort indices[3] = {...}
[...]
glDrawElements(..., 3, GL_UNSIGNED_SHORT, ...);

Note that trying to use GL_UNSIGNED_INT as the type parameter on an implementation without support for GL_OES_element_index_uint should just result in an GL_INVALID_ENUM error. You should add some error checks at least for debugging.