Question

I’m working on a 2D engine in C++ at the moment.

I’ve run into a problem which I seem to believe I’ve come up against once before, but have since forgotten how I fixed it.

The engine is cross platform ( Win, OSX, Linux ) and to accomplish this I am using GLFW as a base.

When doing the normal texturing thing I end up with this :

As you can see the texturing isn’t right ( as the image is supposed to be a simple Image of me ).

Using geDebugger I can confirm that the image being buffered to the GPU is correct, but some how it is ending up as you see in the Image.

I’ll include some cuts of relevant code below, but should you want more info feel free to ask.

-Buffer Generation Code

glGenVertexArrays( 1, &_vao );
// Generate Buffers and so on.
glBindVertexArray( _vao );

glGenBuffers( 1, &_vboVertices );
glBindBuffer( GL_ARRAY_BUFFER, _vboVertices );
glBufferData( GL_ARRAY_BUFFER, sizeof(GLfloat) * 3 * _numVertices, _vertices, GL_STATIC_DRAW );

glGenBuffers( 1, &_vboTexCoords );
glBindBuffer( GL_ARRAY_BUFFER, _vboTexCoords );
glBufferData( GL_ARRAY_BUFFER, sizeof(GLfloat) * 2 * _numVertices, _texCoords, GL_STATIC_DRAW );

glGenBuffers( 1, &_vboIndices );
glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, _vboIndices );
glBufferData( GL_ELEMENT_ARRAY_BUFFER, sizeof(GLint) * _numIndices, _indices, GL_STATIC_DRAW );

-Render Code

glm::mat4 modelViewProjMatrix = projMatrix * viewMatrix * modelMatrix;

ShaderResource * shader = ShaderManager::GetInstance()->GetShader( _shaderName.c_str() );
TextureResource * texture = TextureManager::GetInstance()->GetTexture( _textureName.c_str() );

shader->BindShader();

// Bind VAO
glBindVertexArray( _vao );

// Bind all VBO's
glBindBuffer( GL_ARRAY_BUFFER, _vboVertices );
GLint posLocation = shader->GetAttribLocation("in_position");
glVertexAttribPointer( posLocation, 3, GL_FLOAT, GL_FALSE, 0, (void*)0 );
GLint texCoordLocation = shader->GetAttribLocation("in_texCoord");
glVertexAttribPointer( texCoordLocation, 2, GL_FLOAT, GL_FALSE, 0, (void*)0 );
glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, _vboIndices );

// Enable VBO Pointers
glEnableVertexAttribArray( posLocation );
glEnableVertexAttribArray( texCoordLocation );

// Find and assign Uniforms
GLint MVPMatrixLocation = shader->GetUniformLocation("in_MVPMatrix");
GLint colourLocation = shader->GetUniformLocation("in_colour");
GLint textureLocation = shader->GetUniformLocation("texMap");

glUniformMatrix4fv( MVPMatrixLocation, 1, GL_FALSE, glm::value_ptr( modelViewProjMatrix ) );
glUniform4fv( colourLocation, 1, glm::value_ptr( _colour ) );

// Texture Uniform
if( texture != 0 )
{
    glActiveTexture( GL_TEXTURE0 );
    glUniform1i( textureLocation, 0 );
    glBindTexture( GL_TEXTURE_2D, texture->GetTextureId() );
}

glDrawElements( GL_TRIANGLES, _numIndices, GL_UNSIGNED_INT, (void*) 0 );

glDisableVertexAttribArray( posLocation );
glDisableVertexAttribArray( texCoordLocation );

shader->UnbindShader();

glBindVertexArray( 0 );

-Vert Shader

#version 150

in vec3 in_position;
in vec2 in_texCoord;

out vec4 out_colour;
smooth out vec2 out_texCoord;

uniform vec4 in_colour;
uniform mat4 in_MVPMatrix;

void main()
{
out_colour = in_colour;
out_texCoord = in_texCoord;

    gl_Position = in_MVPMatrix * vec4( in_position, 1.0 );
}

-Frag Shader

#version 150

in vec4 out_colour;
smooth in vec2 out_texCoord;

out vec4 fragColor;

uniform sampler2D texMap;

void main()
{
    vec4 diffuseTexel = texture2D( texMap, out_texCoord );

    fragColor = out_colour * diffuseTexel;
} 

Answer 1

glVertexAttribPointer( posLocation, 3, GL_FLOAT, GL_FALSE, 0, (void*)0 );
glVertexAttribPointer( texCoordLocation, 2, GL_FLOAT, GL_FALSE, 0, (void*)0 );

This means that both the positions and texture coordinates come from the same locations in the buffer. That they overlap.

You seem to want them to come from different buffer objects. That means you have to bind a new buffer to GL_ARRAY_BUFFER between your first and second glVertexAttribPointer calls.