Vertex texture Fetch (Texture read in vertex shader)

Question

New to Opengl and GLSL.

I am using OpenGL es 3.0 and my GLSL version #version 300 es.

i want to get pixel(ARGB data) at every position in my vertex shader(vertex texture fetch). i have verified that my Android tablet supports vertex texture fetch.

Now i pass in the texture(image) and Texture coordinates to the vertex shader and execute

GLES30.glDrawArrays(GLES30.GL_TRIANGLE_STRIP, 0, 4);

Is this the right way or should i use GL_POINTS . if i am using GL_POINTS how to pass the texture cooordinate?

could you provide any samples/example code that does a full pixel read(ARGB) in the vertex shader.

attaching my vertex shader

uniform sampler2D sTexture; 
in vec4 aTextureCoord;
out vec3 colorFactor;
vec2 vTextureCoord;
vec4 tex;
void main() 
{
   vTextureCoord = aTextureCoord.xy;
   tex =  texture(sTexture,vTextureCoord);
   float luminance = 0.299 * tex.r + 0.587 * tex.g + 0.114 * tex.b;
   colorFactor = vec3(1.0, 1.0, 1.0);
   gl_Position = vec4(-1.0 + (luminance * 0.00784313725), 0.0, 0.0,      1.0); 
   gl_PointSize = 1.0;
};

My texture coordinates passed are {0.f,1.f}
{1.f,1.f} {0.f,0.f} {1.f,0.f}

and the shader is triggered by

GLES30.glDrawArrays(GLES30.GL_TRIANGLE_STRIP, 0, 4);

Tommy Tommy · Accepted Answer · 2016-05-26T13:21:56

Just declare a sampler and sample it exactly as per usual. E.g.

"#version 150\n"

in vec4 position;
in vec2 texCoordinate;

uniform sampler2D texID;
uniform mat4 modelViewProjection;

void main()
{
    gl_Position = modelViewProjection * (position + texture(texID, texCoordinate));
}

That will sample a 4d vector from the texture unit texID at location texCoordinate, using that to perturb position prior to applying the model-view-projection matrix. The type of geometry you're drawing makes no difference.

Vertex texture Fetch (Texture read in vertex shader)

2 Answers