Passing 2D array into GLES opengl shader

Question

I have a 2D array of floats (in this case it represents a 256 color palette with R G B values)

static float[][] glColorPaletteArray = new float[256][3];

I fill the array and now want to pass it to GLES. How do I pass a 2D array in android? I try

GLES20.glUniform3fv(paletteLoc,256,glColorPaletteArray,0);

but it complains about expecting a 1D array (found float[][] expecting float[]).

The shader is expecting a vec3 uniform, ie

uniform vec3 palette[256];

so I need to keep the 2D array so the RGB components are separate floats.

What is the secret to getting the 2D array passed correctly to the GLES shader so I can then access the RGB values in the shader by using

int red = palette[100].r;

BDL · Accepted Answer · 2015-10-16 07:44:26Z

1

The short answer is: You cannot pass a 2D array to a shader.

In order to pass a 2D array to OpenGL, one has to flatten the array. This is relatively easy and can, e.g., be done as follows:

static float[][] glColorPaletteArray = new float[256][3];
static float[] openglArray = new float[256*3];

for (int i = 0; i < 256; i++)
    for (int j = 0; j < 3; j++)
        openglArray[i * 3 + j] = glColorPalletArray[i][j];

But I would suggest that, if possible, you define the array in 1D at first hand.

answered Oct 16, 2015 at 7:44

BDL

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2 Comments

Some1Else Over a year ago

OK, but once converted to 1D will the shader (expecting vec3 entries) know how to extract the RGB components of each of the 256 colors?

BDL Over a year ago

Yes it will. Always 3 consecutive floats will be used as one vec3.

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