Question

I have been working on a game and encountered a really weird problem. Game renders at round 4k fps on my setup but after drawing a coloured square covering the whole screen + a little more as a background it drops down to 3k fps. Changing the size of the square to a smaller one makes the problem disappear.

Im drawing 40k triangles and particle systems already.

The square is a triangle strip loaded in a VBO.

GLfloat vBackground[4][3] = {
        { 0.0f, 0.0f, 0.0f },
        { 16.0f, 0.0f, 0.0f },

        { 0.0f, 16.0f, 0.0f },
        { 16.0f, 16.0f, 0.0f }
};

Im using the simplest shaders possible:

vertex
#version 140

#extension GL_ARB_explicit_attrib_location : enable

layout (location = 0) in vec4 vVertex;

uniform mat4 mvpMatrix;
uniform vec4 inColor;

varying vec4 color;

void main(void)
{
    color = inColor;
    gl_Position = mvpMatrix * vVertex;
}

fragment
#version 140

out vec4 vFragColor;

varying vec4 color;

void main(void) 
{
    vFragColor = color;
}

Is the pixel fill rate of the graphics card just too slow?

Answer 1

4 thousand FPS means it takes you 0.25 milliseconds to render a frame. 3 thousand FPS means it takes you 0.33 milliseconds to render. A total difference of 0.08 milliseconds, or 80 microseconds.

I wouldn’t be worried about it. Your card isn’t “too slow”; you’re too sensitive to minor time differences.