I'm working on some examples, and I was trying to pass a texture to a shader.
To build a VAO, I have this piece of code:
void PlaneShaderProgram::BuildVAO()
{
// Generate and bind the vertex array object
glGenVertexArrays(1, &_vao);
glBindVertexArray(_vao);
// Generate and bind the vertex buffer object
glGenBuffers(1, &_vbo);
glBindBuffer(GL_ARRAY_BUFFER, _vbo);
glBufferData(GL_ARRAY_BUFFER, 12 * sizeof(GLfloat), _coordinates, GL_STATIC_DRAW);
// Generate and bind the index buffer object
glGenBuffers(1, &_ibo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ibo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, 6 * sizeof(GLuint), _indexes, GL_STATIC_DRAW);
// Generate and bind texture
_texture = LoadTexture("floor.bmp");
LoadAttributeVariables();
glBindVertexArray(0);
}
This is how I load the shader attributes:
void PlaneShaderProgram::LoadAttributeVariables()
{
GLuint VertexPosition_location = glGetAttribLocation(GetProgramID(), "vPosition");
glEnableVertexAttribArray(VertexPosition_location);
glVertexAttribPointer(VertexPosition_location, 3, GL_FLOAT, GL_FALSE, 0, 0);
}
void PlaneShaderProgram::LoadUniformVariables()
{
// OpenGL Matrices
GLuint ModelViewProjection_location = glGetUniformLocation(GetProgramID(), "mvpMatrix");
glUniformMatrix4fv(ModelViewProjection_location, 1, GL_FALSE, glm::value_ptr(_ModelViewProjection));
// Floor texture
// glActiveTexture(GL_TEXTURE0);
// glBindTexture(GL_TEXTURE_2D, _texture);
// GLint Texture_location = glGetUniformLocation(GetProgramID(), "texture");
// glUniform1i(Texture_location, 0);
}
And my LoatTexture
:
GLuint ProgramManager::LoadTexture(const char* imagepath)
{
unsigned char * data = LoadBMP(imagepath, &width, &height);
GLuint textureID;
glGenTextures(1, &textureID);
glBindTexture(GL_TEXTURE_2D, textureID);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_BGR, GL_UNSIGNED_BYTE, data);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
return textureID;
}
Finally, my draw function, which is called in the OpenGL main loop, is the following:
void PlaneShaderProgram::DrawPlane(const glm::mat4 &Projection, const glm::mat4 &ModelView)
{
_ModelViewProjection = Projection * ModelView;
_ModelView = ModelView;
Bind();
glBindVertexArray(_vao);
LoadUniformVariables();
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glBindVertexArray(0);
UnBind();
}
What I didn't get is that even if I didn't set the uniform texture (commented in the code) used by my shader, the plane is still draw using the texture. This makes no sense for me. Once the shader requires a sample2D, I think this shouldn't work and return some error.
Vertex Shader:
uniform mat4 mvpMatrix;
in vec4 vPosition;
smooth out vec2 uvCoord;
void main()
{
uvCoord = vPosition.xz;
gl_Position = mvpMatrix * vPosition;
}
Frag Shader:
uniform sampler2D texture;
in vec2 uvCoord;
out vec4 fragColor;
void main()
{
fragColor.rgb = texture(texture, uvCoord).rgb;
};
Am I missing something? Somehow this works I don't understand why, but I really like to.