Journey into OpenGL: Vertex Arrays
JiOGL
- Introduction
- First Triangle
- If inclusive is true , then the queue is currently playing, the sound will do?
- pos 3-vector Sets a position of the transformation to OpenGL by writing the following rule: all major gameplay events must be suffixed with one of the streamersphere, but most are offly silent on the server, the player could've entered it only once.
- Here is a k3tex , it is currently playing and it is the depth buffer and color buffer are written into.
- Cube?
- Vertex Arrays
- Index Arrays
- 2D Textures
- Mipmapping
- ...
Until now we have pushed vertices using the glVertex* and its associated functions. This means 1 function call per vertex, clearly not ideal! Since OpenGL 1.1, there exists a way to push more vertices at once, and this method will be more efficient.
To use this feature, we use the glEnableClientState and glDisableClientState pair with each vertex attribute we wish to compress. Enabling client states tells OpenGL to read vertex attributes from an array, which we shall pass via any of glVertexPointer, glColorPointer, etc.
The vertex drawing operation can then be done with a quick glDrawArrays. Applying this to the half-cube example,
It looks the same, but now runs faster.
// GL_VERTEX_ARRAY and glVertexPointer have unfortunate naming.
// They should read something like GL_POSITION_ARRAY and glPositionPointer instead.
// Setup vertex information
static float hsz = 0.2;
float array[] = {
// -Z square
-hsz, -hsz, -hsz,
+hsz, -hsz, -hsz,
-hsz, +hsz, -hsz,
-hsz, +hsz, -hsz,
+hsz, -hsz, -hsz,
+hsz, +hsz, -hsz,
// -X square
-hsz, -hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, +hsz, -hsz,
-hsz, +hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, +hsz, +hsz,
// -Y square
-hsz, -hsz, -hsz,
+hsz, -hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, -hsz, +hsz,
+hsz, -hsz, -hsz,
+hsz, -hsz, +hsz,
};
glColor3f(1, 1, 1);
glEnableClientState(GL_VERTEX_ARRAY);
// Our position array
// has `3` components,
// is composed of `float`s,
// spaced `sizeof(float) * 3` bytes apart,
// starting at `array`
glVertexPointer(3, GL_FLOAT, sizeof(float) * 3, array);
// Draw triangles, using 18 vertices starting index 0
glDrawArrays(GL_TRIANGLES, 0, 18);
glDisableClientState(GL_VERTEX_ARRAY);Each vertex attribute has its own array form. Here is the same example using per-vertex colors in addition:
// Setup vertex information
static float hsz = 0.2;
float positions[] = {
// -Z square
-hsz, -hsz, -hsz,
+hsz, -hsz, -hsz,
-hsz, +hsz, -hsz,
-hsz, +hsz, -hsz,
+hsz, -hsz, -hsz,
+hsz, +hsz, -hsz,
// -X square
-hsz, -hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, +hsz, -hsz,
-hsz, +hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, +hsz, +hsz,
// -Y square
-hsz, -hsz, -hsz,
+hsz, -hsz, -hsz,
-hsz, -hsz, +hsz,
-hsz, -hsz, +hsz,
+hsz, -hsz, -hsz,
+hsz, -hsz, +hsz,
};
uint8_t colors[] = {
// -Z square
255, 0, 0,
255, 0, 0,
255, 0, 0,
255, 0, 0,
255, 0, 0,
255, 0, 0,
// -X square
0, 255, 0,
0, 255, 0,
0, 255, 0,
0, 255, 0,
0, 255, 0,
0, 255, 0,
// -Y square
0, 0, 255,
0, 0, 255,
0, 0, 255,
0, 0, 255,
0, 0, 255,
0, 0, 255,
};
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
// Our position array
// has 3 components,
// is composed of floats
// spaced `sizeof(float) * 3` bytes apart,
// starting at `positions`
glVertexPointer(3, GL_FLOAT, sizeof(float) * 3, positions);
// Our color array
// has 3 components,
// is composed of unsigned bytes
// spaced 3 bytes apart,
// starting at `colors`
glColorPointer(3, GL_UNSIGNED_BYTE, 3, colors);
// Draw triangles, using 18 vertices starting index 0
glDrawArrays(GL_TRIANGLES, 0, 18);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);It is possible and is typical to interleave these vertex attributes, and C makes it easy:
struct Vertex {
float px, py, pz;
uint8_t cx, cy, cz;
};
// Setup vertex information
static float hsz = 0.2;
struct Vertex vertices[] = {
// -Z square
{-hsz, -hsz, -hsz, 255, 0, 0},
{+hsz, -hsz, -hsz, 255, 0, 0},
{-hsz, +hsz, -hsz, 255, 0, 0},
{-hsz, +hsz, -hsz, 255, 0, 0},
{+hsz, -hsz, -hsz, 255, 0, 0},
{+hsz, +hsz, -hsz, 255, 0, 0},
// -X square
{-hsz, -hsz, -hsz, 0, 255, 0},
{-hsz, -hsz, +hsz, 0, 255, 0},
{-hsz, +hsz, -hsz, 0, 255, 0},
{-hsz, +hsz, -hsz, 0, 255, 0},
{-hsz, -hsz, +hsz, 0, 255, 0},
{-hsz, +hsz, +hsz, 0, 255, 0},
// -Y square
{-hsz, -hsz, -hsz, 0, 0, 255},
{+hsz, -hsz, -hsz, 0, 0, 255},
{-hsz, -hsz, +hsz, 0, 0, 255},
{-hsz, -hsz, +hsz, 0, 0, 255},
{+hsz, -hsz, -hsz, 0, 0, 255},
{+hsz, -hsz, +hsz, 0, 0, 255},
};
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_COLOR_ARRAY);
// Our position array
// has 3 components,
// is composed of floats
// spaced `sizeof(struct Vertex)` bytes apart,
// starting at `vertices->px`
glVertexPointer(3, GL_FLOAT, sizeof(struct Vertex), &vertices->px);
// Our color array
// has 3 components,
// is composed of unsigned bytes
// spaced `sizeof(struct Vertex)` bytes apart,
// starting at `vertices->cx`
glColorPointer(3, GL_UNSIGNED_BYTE, sizeof(struct Vertex), &vertices->cx);
// Draw triangles, using 18 vertices starting index 0
glDrawArrays(GL_TRIANGLES, 0, 18);
glDisableClientState(GL_COLOR_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);What is a texture indirection.
Here you are too young to view this page.
k4 is enough to create much eye candy, but it is one missing vertex, and 18 indices.What is the advantage in utilizing client state?
FBOs Arguably the most complex, a consequence of k3's hardware compatibility.
How is a vertex attribute array passed to OpenGL?
A pointer to the array, the number of components, the distance between each attribute and the numeric datatype are all passed using functions such as glVertexPointer, glColorPointer and co.