Shaders Question about Texture Coordinates

[Roscoe.Zhao]

Hi,
I'm trying to make a shader where I need to get some RGB values from a texture input from a surface (actually it's an output of another shader)
I tried something like this:

varying vec4 v_vColour;
varying vec2 v_vTexcoord;

uniform sampler2D Texture;
// The 'texture surface'
// This is from another shader's output, like this: texture_set_stage(uTexture,surface_get_texture(sTexture));

void main() {
    gl_FragColor =  texture2D(Texture, v_vTexcoord);
}

I tried this and expected it will draw the 'texture surface', but it gives a black screen.
I tried to draw the texture surface using draw_surface_stretched() it's normal, not empty.
Maybe I need to somehow calculate a new texture coordinate for that texture surface?
I know I could use the uvs values and v_vTexcoord to calculate the corresponding texcoords if I'm drawing a sprite, but I don't know how to deal with surfaces.
I can't find a function similar to sprite_get_uvs() for surfaces

Any help would be appreciated

 

[flyingsaucerinvasion]

Hi. What are you drawing? And what are you drawing onto?

Surfaces don't have a get_uvs function. The left side of a surface always has x texture coordinate of 0, right is 1. The top side of a surface has y texture coordinate 0, bottom is 1.

 

[Roscoe.Zhao]

In that example, I'm drawing a surface to another surface
the two surfaces actually have same size.
I don't know why but the codes above gives a black screen..

 

[flyingsaucerinvasion]

You should show the drawing code.

 

[Roscoe.Zhao]

// In draw event

surface_set_target(sTexture);
shader_set(shd_initial);
shader_set_uniform_f(shader_get_uniform(shd_initial,"D"),D);
draw_surface(sTexture,0,0);
shader_reset();
surface_reset_target();

// If I draw sTexture here, and comment-out the rest of code, it will draw sTexture surface normally.

surface_set_target(sUpdate);
shader_set(shd_update);
texture_set_stage(sUpdate,surface_get_texture(sTexture));
draw_surface(sUpdate,0,0);
shader_reset();
surface_reset_target();

draw_surface_stretched(sUpdate,0,0,640,480); // Draws black screen

 

[flyingsaucerinvasion]

You're not supposed to draw surfaces onto themselves. Not sure on the technical details, but gpus apparently have problems sampling textures they are simultaneously writing to. Or something along those lines.


I don't know if that is the cause of your problem, since as you say sTexture will show up.

EDIT:

texture_set_stage(sUpdate,surface_get_texture(sTexture));

sUpdate is not a sampler index, is it?

Look up shader_get_sampler_index

 

[Roscoe.Zhao]

But actually I'll need to continuously update that surface,
Can I draw it to a temporary one, then use surface_copy() to copy it back to that surface?

 

[Roscoe.Zhao]

You're not supposed to draw surfaces onto themselves. Not sure on the technical details, but gpus apparently have problems sampling textures they are simultaneously writing to. Or something along those lines.


I don't know if that is the cause of your problem, since as you say sTexture will show up.

EDIT:

texture_set_stage(sUpdate,surface_get_texture(sTexture));

sUpdate is not a sampler index, is it?

Look up shader_get_sampler_index

Thank you very much! Solved it!