CODEWITHSUNDEEP
openglopengl-es-2.0glsles
Yoshi
Yoshi

Reputation: 583

Port from OpenGL to GLES 2.0

I have used https://github.com/akrinke/Font-Stash.git for some desktop applications. Now I want to use it on a raspberry Pi which use gles2. I looked into the code and see the only path that don't work on gles is flush_draw function:

glBindTexture(GL_TEXTURE_2D, texture->id);
glEnable(GL_TEXTURE_2D);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glVertexPointer(2, GL_FLOAT, VERT_STRIDE, texture->verts);
glTexCoordPointer(2, GL_FLOAT, VERT_STRIDE, texture->verts+2);
glDrawArrays(GL_TRIANGLES, 0, texture->nverts);
glDisable(GL_TEXTURE_2D);
glDisableClientState(GL_VERTEX_ARRAY);
glDisableClientState(GL_TEXTURE_COORD_ARRAY);

I'm trying to port to gles to this:

glBindTexture(GL_TEXTURE_2D, texture->id);
glEnable(GL_TEXTURE_2D);
GLint position_index = get_attrib(stash->program, "position");
glEnableVertexAttribArray(position_index);
glVertexAttribPointer (position_index, 2, GL_FLOAT, GL_FALSE, VERT_STRIDE, texture->verts);
GLint texture_coord_index = get_attrib(stash->program, "texCoord");
glEnableVertexAttribArray(texture_coord_index);
glVertexAttribPointer (texture_coord_index, 2, GL_FLOAT, GL_FALSE, VERT_STRIDE, texture->verts + 2);
GLint texture_index = get_uniform(stash->program, "texture");
glUniform1i(texture_index, 0);
glDrawArrays(GL_TRIANGLES, 0, texture->nverts);
glDisable(GL_TEXTURE_2D);

with vertex sl

attribute vec4 position;
attribute vec2 texCoord;
varying vec2 texCoordVar;
void main() {
  gl_Position = position;
  texCoordVar = texCoord;
}

and fragment sl

precision mediump float;        // set default precision for floats to medium
uniform sampler2D texture;      // shader texture uniform
varying vec2 texCoordVar;       // fragment texture coordinate varying
void main() {
  // sample the texture at the interpolated texture coordinate
  // and write it to gl_FragColor
  gl_FragColor = texture2D( texture, texCoordVar);
}

but I can't get anything, nothing on screen.

Can anybody show me what's wrong with my code?

Upvotes: 1

Views: 2059

Answers (2)

chrisvarnz
chrisvarnz

Reputation: 457

glEnable(GL_TEXTURE_2D), is not valid GLES2 btw. Also you're not doing any manipulation of the position in your vertex shader, so unless the coordinates are guaranteed to sit within the frustum and you're just passing them through to the rasterizer, then you are leaving it to luck as to whether or not they end up in the frustum. Are you sure you've accounted for everything the fixed function pipe used to handle regarding transforms?

Upvotes: 0

Vasaka
Vasaka

Reputation: 2022

You should setup transformations in your vertex shader. Best way to port fixed function OpenGL app is to write vertex and pixel shader that replicate fixed pipeline with transformations set as uniforms and set those uniforms every time transform is changed.

Upvotes: 1

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