Using GL_SHORT instead of GL_FLOAT in an OpenGL ES vertex array

Question

I have this vertex cube array

float vertex_coordinates [] = {

-12.43796, -12.43796, 12.43796, -12.43796, 12.43796, 12.43796, 12.43796, 12.43796, 12.43796,
12.43796, 12.43796, 12.43796, 12.43796, -12.43796, 12.43796, -12.43796, -12.43796, 12.43796,
12.43796, -12.43796, -12.43796, 12.43796, 12.43796, -12.43796, -12.43796, 12.43796, -12.43796,
-12.43796, 12.43796, -12.43796, -12.43796, -12.43796, -12.43796, 12.43796, -12.43796, -12.43796,
-12.43796, -12.43796, -12.43796, -12.43796, 12.43796, -12.43796, -12.43796, 12.43796, 12.43796,
-12.43796, 12.43796, 12.43796, -12.43796, -12.43796, 12.43796, -12.43796, -12.43796, -12.43796,
12.43796, -12.43796, 12.43796, 12.43796, 12.43796, 12.43796, 12.43796, 12.43796, -12.43796,
12.43796, 12.43796, -12.43796, 12.43796, -12.43796, -12.43796, 12.43796, -12.43796, 12.43796,
-12.43796, 12.43796, 12.43796, -12.43796, 12.43796, -12.43796, 12.43796, 12.43796, -12.43796,
12.43796, 12.43796, -12.43796, 12.43796, 12.43796, 12.43796, -12.43796, 12.43796, 12.43796,
-12.43796, -12.43796, -12.43796, -12.43796, -12.43796, 12.43796, 12.43796, -12.43796, 12.43796,
12.43796, -12.43796, 12.43796, 12.43796, -12.43796, -12.43796, -12.43796, -12.43796, -12.43796,

};

I am currently doing this with

glVertexPointer(3, GL_FLOAT, 0, vertex__coordinates);

// texture pointer ...

// colour pointer

glDrawArrays(GL_TRIANGLES, 0, size);

How can I switch to converting an array of vertices into values ​​that will be displayed in exactly the same cube, but instead using GL_SHORTglVertexPointer as the second parameter to speed up my code?

Answer 1

At the pre-processing step, we calculate the min and max of the object and use it to maximize the accuracy in the short:

float modelMin[3] = {FLT_MAX, FLT_MAX, FLT_MAX}; //or std::numeric_limits<float>
float modelMax[3] = {-FLT_MAX, -FLT_MAX, -FLT_MAX};
for (int i = 0; i < size; ++i) {
    for (int j = 0; j < 3; ++j) {
        const float v = vertex_coordinates[i * 3 + j];
        modelMin[j] = std::min(modelMin[j], v);
        modelMax[j] = std::max(modelMax[j], v);
    }
}

short* short_coordinates = new short[size * 3];
for (int i = 0; i < size; ++i) {
    for (int j = 0; j < 3; ++j) {
        const float src = vertex_coordinates[i * 3 + j];
        short& dst = short_coordinats[i * 3 + j];
        dst = (short)floorf(((src - modelMin[j]) / (modelMax[j] - modelMin[j])) * 65536.0f - 32768.0f + 0.5f);
    }
}

And when drawing, we do the following:

const float scale[3], bias[3];
for (int i = 0; i < 3; ++i) {
    scale[i] = (modelMax[j] - modelMin[j]) / 65536.0f;
    bias[i] = (32768.0f / 65536.0f) * (modelMax[j] - modelMin[j]) + modelMin[j];
}

glTranslatef(bias[0], bias[1], bias[2]);
glScalef(scale[0], scale[1], scale[2]);
glVertexPointer(3, GL_SHORT, 0, short_coordinates);
glDrawArrays(GL_TRIANGLES, 0, size);

/ AB

Answer 2

instead of (+ -) 12.43796 use (+ -) 1

glScalef 12.43796

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