CODEWITHSUNDEEP
openglvbo
igal k
igal k

Reputation: 1914

Making opengl work (paint)faster

im trying to paint 512*512 points , which each point uses its neighbors. for example

glBegin(GL_TRIANGLE_STRIP);
glVertex(x,y,z);
glVertex(x+1,y,z);
glVertex(x,y,z+1);
glVertex(x+1,y,z+1);
glEnd();

the problem is that it works quite slow , i know i can use VBO (working with CUDA aswell) but im not sure how to define the VBO to work with GL_TRIANGLE_STRIP and how to set the painting order of the vertices.

Upvotes: 3

Views: 534

Answers (1)

datenwolf
datenwolf

Reputation: 162367

One way to use VBOs (there are variants, using the old Vertex Array API, directly uploading the data with glBufferData and other nice things).

GLuint vbo; // this variable becomes a handles, keep them safe
GLuint idx;

glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(GLfloat)*512*512*3, NULL, GL_STATIC_DRAW);
GLfloat *vbuf = glMapBuffer(GL_ARRAY_BUFFER, GL_WRITE);
fill_with_vertex_data(vbo);
glUnmapBuffer(GL_ARRAY_BUFFER);

glGenBuffers(1, &idx);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(GLuint)*512*512*4, NULL, GL_STATIC_DRAW);
GLfloat *ibuf = glMapBuffer(GL_ELEMENT_ARRAY_BUFFER, GL_WRITE);
GLuint restart_index = 0xffff;
fill_with_indices_restart(ibuf, restart_index); // 0xffff is the restart index to be used, delimiting each triangle strip.
glUnmapBuffer(GL_ELEMENT_ARRAY_BUFFER);

/* ... */

glEnableVertexAttribArray(vertex_position_location);

glBindBuffer(GL_ARRAY_BUFFER, vbo);
glVertexAttrxPointer(vertex_position_location, 3, GL_FLOAT, GL_FALSE, 0, 0);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, idx);
glPrimitiveRestartIndex(restart_index);
glDrawElements(GL_TRIANGLE_STRIP, 0, count, 0);

Upvotes: 2

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