Luminance Histogram Calculation In Gpu-android Opengl Es 3.0

For Luminace histogram calculation I have used the code from the project GPU image ios by Brad Larson. He has used blending for Histogram calculation. Attaching the Vertex and Fr

Solution 1:

I'm using C and desktop GL, but here's the gist of it :

Vertex shader

#version 330
layout (location = 0) in vec2 inPosition;
voidmain()
{
    int x = compute the bin (0 to 255) from inPosition;

    gl_Position = vec4(
        -1.0 + ((x + 0.5) / 128.0),
        0.5,
        0.0,
        1.0
    );
}

Fragment shader

#version 330
out vec4 outputColor;
voidmain()
{
    outputColor = vec4(1.0, 1.0, 1.0, 1.0);
}

Init:

glGenTextures(1, &tex);
glGenFramebuffers(1, &fbo);

glActiveTexture(GL_TEXTURE0);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexStorage2D(GL_TEXTURE_2D, 1, GL_R32F, 256, 1);

glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, tex, 0);

Drawing :

/* Upload data */
glBufferData(GL_ARRAY_BUFFER, num_input_data * 2 * sizeof(float), input_data_ptr, GL_STREAM_DRAW);

/* Clear buffer */constfloat zero[4] = { 0.0f, 0.0f, 0.0f, 0.0f };
glClearBufferfv(GL_COLOR, 0, zero);

/* Init viewport */
glViewport(0, 0, 256, 1);

/* Draw */
glDrawArrays(GL_POINTS, 0, num_input_data);

For brievety I only put the init code for the resulting buffer, all the VBO/VAO init/binding has been skipped