CODEWITHSUNDEEP
c++openglshader
Hugius
Hugius

Reputation: 380

OpenGL Trying to render 2 textures, but only 1 does?

I am trying to render 2 textures in OpenGL 3. I created two arrays of vertices of GLfloat type,generated and bound the buffers etc.

Note: The texture loading function is working fine,I have already loaded a texture before, now I just need 2 textures rendered at the same time.

Then I load my textures like this:

GLuint grass = texture.loadTexture("grass.bmp");
GLuint grassLoc = glGetUniformLocation(programID, "grassSampler");
glUniform1i(grassLoc, 0);

GLuint crate = texture.loadTexture("crate.bmp");
GLuint crateLoc = glGetUniformLocation(programID, "crateSampler");
glUniform1i(crateLoc, 1);

This is how I draw them:

glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, grass);
glDrawArrays(GL_TRIANGLES, 0, 6); 

glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, crate);
glDrawArrays(GL_TRIANGLES, 2, 6);

Vertex shader:

#version 330 core

layout(location = 0) in vec3 grassPosition;
layout(location = 1) in vec2 grassUvPosition;

layout(location = 2) in vec3 cratePosition;
layout(location = 3) in vec2 crateUvPosition;

out vec2 grassUV;
out vec2 crateUV;

uniform mat4 MVP;

void main(){
    gl_Position =  MVP * vec4(grassPosition,1);
    gl_Position =  MVP * vec4(cratePosition,1);
    grassUV = grassUvPosition;
    crateUV = crateUvPosition;
}

Fragment shader:

#version 330 core

in vec2 grassUV;
in vec2 crateUV;

out vec3 grassColor;
out vec3 crateColor;

uniform sampler2D grassSampler;
uniform sampler2D crateSampler;

void main(){
    crateColor = texture(grassSampler, grassUV).rgb;
    grassColor = texture(crateSampler, crateUV).rgb;
}

Can anyone see what I am doing wrong?

EDIT: I am trying to render 2 different textures on 2 different VAOs

Upvotes: 1

Views: 597

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 473182

You're kinda doing everything wrong; it's hard to pick out one thing.

Your shaders look like they're tying to take two positions and two texture coordinates, presumably generate two triangles, then sample from two textures and write colors to two different images.

That's not how it works. Unless you use a geometry shader (and please do not take that as an endorsement), your call to glDrawArrays(GL_TRIANGLES, 0, 6); will render exactly 2 triangles, no matter what your VS or FS's say.

A vertex has only one position. Writing to gl_Position twice will simply overwrite the previous value, just like writing to any variable twice in C++ would. And the number of triangles to be rendered is defined by the number of vertices. A vertex shader cannot create vertices. It can't even destroy them (though, through gl_CullDistance, it can potentially cull whole primitives).

It is not clear what you mean by "I just need 2 textures rendered at the same time." Or more to the point, what "at the same time" refers to. I don't know what your code ought to be trying to do.

Given the data your vertex shader expects, it looks like you have two separate sets of triangles, with their own positions and texture coordinates. You want to render one set of triangles with one texture, then render another set with a different texture.

So... do that. Instead of having your VAOs send 2 positions and 2 texture coordinates, send just one. Your VS should also take one position/texcoord, and your FS should similarly take a single texture and write to a single output. The difference will be determined by what VAO is currently active and which texture is bound to texture unit 0 at the time you issue the render call.

If you truly intend to write to different output images, the way your FS suggests, then change FBOs between rendering as well.

If however, your goal is to have the same triangle use two textures with two mappings, writing separate results to two images, you can do that too. The difference is that you only provide a single position, and textures must be bound to both texture units 0 and 1 when you issue your rendering command.

Upvotes: 3

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