Comment faire de l'instanciation de la bonne façon en OpenGL.

Je suis en train d'utiliser les VBO et l'Instanciation mécanisme le plus efficace. J'ai un monde basé sur les voxels et je tiens à les dessiner en utilisant le moins possible nombre de tirage-des appels. Le code ci-dessous prépare VBO avec un quad:

void VoxelView::initVBOs() {
/*--------------------- Main OpenGL Program ---------------------*/
/* Vertices of a triangle (counter-clockwise winding) */
float data[6][3] = {
//Left bottom triangle
{ -0.5f, 0.5f, 0.0f  },
{ -0.5f, -0.5f, 0.0f },
{ 0.5f, -0.5f, 0.0f  },
//Right top triangle
{ 0.5f, -0.5f, 0.0f  },
{ 0.5f, 0.5f, 0.0f   },
{ -0.5f, 0.5f, 0.0f  }
};
/*---------------------- Initialise VBO - (Note: do only once, at start of program) ---------------------*/
/* Create a new VBO and use the variable "triangleVBO" to store the VBO id */
glGenBuffers(1, &triangleVBO);
/* Make the new VBO active */
glBindBuffer(GL_ARRAY_BUFFER, triangleVBO);
/* Upload vertex data to the video device */
glBufferData(GL_ARRAY_BUFFER, 6 * 3 * sizeof(float), data, GL_STATIC_DRAW);
/* Specify that our coordinate data is going into attribute index 0(shaderAttribute), and contains three floats per vertex */
glVertexAttribPointer(shaderAttribute, 3, GL_FLOAT, GL_FALSE, 0, 0);
/* Enable attribute index 0(shaderAttribute) as being used */
glEnableVertexAttribArray(shaderAttribute);
/* Make the new VBO active. */
glBindBuffer(GL_ARRAY_BUFFER, triangleVBO);
/*-------------------------------------------------------------------------------------------------------*/
/*--------------------- Load Vertex and Fragment shaders from files and compile them --------------------*/
/* Read our shaders into the appropriate buffers */
vertexSource = filetobuf("Shaders/exampleVertexShader1.vert");
fragmentSource = filetobuf("Shaders/exampleFragmentShader1.frag");
/* Assign our handles a "name" to new shader objects */
vertexShader = glCreateShader(GL_VERTEX_SHADER);
fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);
/* Associate the source code buffers with each handle */
glShaderSource(vertexShader, 1, (const GLchar**)&vertexSource, 0);
glShaderSource(fragmentShader, 1, (const GLchar**)&fragmentSource, 0);
/* Free the temporary allocated memory */
free(vertexSource);
free(fragmentSource);
/* Compile our shader objects */
glCompileShader(vertexShader);
glCompileShader(fragmentShader);
/*-------------------------------------------------------------------------------------------------------*/
/*-------------------- Create shader program, attach shaders to it and then link it ---------------------*/
/* Assign our program handle a "name" */
shaderProgram = glCreateProgram();
/* Attach our shaders to our program */
glAttachShader(shaderProgram, vertexShader);
glAttachShader(shaderProgram, fragmentShader);
/* Bind attribute index 0 (shaderAttribute) to in_Position*/
/* "in_Position" will represent "data" array's contents in the vertex shader */
glBindAttribLocation(shaderProgram, shaderAttribute, "in_Position");
/* Link shader program*/
glLinkProgram(shaderProgram); 

Je me suis rendu du quad, de la manière suivante:

void VoxelView::renderVBO()
{
/* Set shader program as being actively used */
glUseProgram(shaderProgram);
/* Set background colour to BLACK */
glClearColor(0.0, 0.0, 0.0, 1.0);
/* Clear background with BLACK colour */
glClear(GL_COLOR_BUFFER_BIT);
/* Actually draw the triangle, giving the number of vertices provided by invoke glDrawArrays
while telling that our data is a triangle and we want to draw 0-3 vertexes
*/
glDrawArrays(GL_TRIANGLES, 0, 6);
}

Je voudrais attirer ce quad (qui utilise le VBO) plusieurs fois à l'aide de l'instanciation mechanizm. Je voudrais qu'elle fe assez simple que je veux le mettre en œuvre des outils plus sophistiqués code. Je sais que je devrais utiliser glDrawElementsInstanced de la méthode à utiliser l'instanciation mais je ne sais pas comment le faire. Quelqu'un sait comment faire?

OriginalL'auteur Paweł Jastrzębski | 2014-02-03